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Human Anatomy and Physiology: Glossary

Human Anatomy and Physiology
Glossary

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  • Project HomeHuman Anatomy and Physiology
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table of contents
  1. Cover
  2. Acknowledgements
  3. Part 1. Levels of Organization
    1. 1. An Introduction to the Human Body
      1. 1.1 Overview of Anatomy and Physiology
      2. 1.2 Structural Organization of the Human Body
      3. 1.3 Functions of Human Life
      4. 1.4 Homeostasis
      5. 1.5 Anatomical Terminology
    2. 2. The Chemical Level of Organization
      1. 2.1 Elements and Atoms: The Building Blocks of Matter
      2. 2.2 Chemical Bonds
      3. 2.3 Chemical Reactions
      4. 2.4 Inorganic Compounds Essential to Human Functioning
      5. 2.5 Organic Compounds Essential to Human Functioning
    3. 3. The Cellular Level of Organization
      1. 3.1 The Cell Membrane
      2. 3.2 The Cytoplasm and Cellular Organelles
      3. 3.3 The Nucleus and DNA Replication
      4. 3.4 Protein Synthesis
      5. 3.5 Cell Growth and Division
      6. 3.6 Cellular Differentiation
    4. 4. The Tissue Level of Organization
      1. 4.1 Types of Tissues
      2. 4.2 Epithelial Tissue
      3. 4.3 Connective Tissue Supports and Protects
      4. 4.4 Muscle Tissue and Motion
      5. 4.5 Nervous Tissue Mediates Perception and Response
  4. Part 2. Support and Movement
    1. 5. The Integumentary System
      1. 5.1 Layers of the Skin
      2. 5.2 Accessory Structures of the Skin
      3. 5.3 Functions of the Integumentary System
    2. 6. Bone Tissue and the Skeletal System
      1. 6.1 The Functions of the Skeletal System
      2. 6.2 Bone Classification
      3. 6.3 Bone Structure
      4. 6.4 Bone Formation and Development
      5. 6.5 Fractures: Bone Repair
      6. 6.6 Nutrition, Hormones, and Bone Tissue
      7. 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems
    3. 7. Axial Skeleton
      1. 7.1 Divisions of the Skeletal System
      2. 7.2 The Skull
      3. 7.3 The Vertebral Column
      4. 7.4 The Thoracic Cage
      5. 7.5 Embryonic Development of the Axial Skeleton
    4. 8. The Appendicular Skeleton
      1. 8.1 The Pectoral Girdles
      2. 8.2 Bones of the Upper Limb
      3. 8.3 The Pelvic Girdle and Pelvis
      4. 8.4 Bones of the Lower Limb
    5. 9. Joints
      1. 9.1 Classification of Joints
      2. 9.2 Fibrous Joints
      3. 9.3 Cartilaginous Joints
      4. 9.4 Synovial Joints
      5. 9.5 Types of Body Movements
      6. 9.6 Anatomy of Selected Synovial Joints
    6. 10. Muscle Tissue
      1. 10.1 Overview of Muscle Tissues
      2. 10.2 Skeletal Muscle
      3. 10.3 Muscle Fibre Contraction and Relaxation
      4. 10.4 Nervous System Control of Muscle Tension
      5. 10.5 Types of Muscle Fibres
      6. 10.6 Cardiac Muscle Tissue
      7. 10.7 Smooth Muscle
    7. 11. The Muscular System
      1. 11.1 Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems
      2. 11.2 Naming Skeletal Muscles
      3. 11.3 Axial Muscles of the Head, Neck, and Back
      4. 11.4 Axial Muscles of the Abdominal Wall and Thorax
      5. 11.5 Muscles of the Pectoral Girdle and Upper Limbs
      6. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
  5. Part 3. Regulation, Integration, and Control
    1. 12. The Nervous System and Nervous Tissue
      1. 12.1 Basic Structure and Function of the Nervous System
      2. 12.2 Nervous Tissue
      3. 12.3 The Functions of Nervous Tissue
      4. 12.4 The Action Potential
      5. 12.5 Communication Between Neurons
    2. 13. Anatomy of the Nervous System
      1. 13.1 The Central Nervous System
      2. 13.2 Circulation and the Central Nervous System
      3. 13.3 The Peripheral Nervous System
    3. 14. The Somatic Nervous System
      1. 14.1 Sensory Perception
      2. 14.2 Central Processing
      3. 14.3 Motor Responses
    4. 15. The Autonomic Nervous System
      1. 15.1 Divisions of the Autonomic Nervous System
      2. 15.2 Autonomic Reflexes and Homeostasis
      3. 15.3 Central Control
    5. 16. The Endocrine System
      1. 16.1 An Overview of the Endocrine System
      2. 16.2 Hormones
      3. 16.3 The Pituitary Gland and Hypothalamus
      4. 16.4 The Thyroid Gland
      5. 16.5 The Parathyroid Glands
      6. 16.6 The Adrenal Glands
      7. 16.7 The Pineal Gland
      8. 16.8 Gonadal and Placental Hormones
      9. 16.9 The Endocrine Pancreas
      10. 16.10 Organs with Secondary Endocrine Functions
  6. Part 4. Fluids and Transport
    1. 17. The Cardiovascular System: Blood
      1. 17.1 An Overview of Blood
      2. 17.2 Production of the Formed Elements
      3. 17.3 Erythrocytes
      4. 17.4 Leukocytes and Platelets
      5. 17.5 Hemostasis
      6. 17.6 Blood Typing
    2. 18. The Cardiovascular System: The Heart
      1. 18.1 Heart Anatomy
      2. 18.2 Cardiac Muscle and Electrical Activity
      3. 18.3 Cardiac Cycle
      4. 18.4 Cardiac Physiology
    3. 19. The Cardiovascular System: Blood Vessels and Circulation
      1. 19.1 Structure and Function of Blood Vessels
      2. 19.2 Blood Flow, Blood Pressure, and Resistance
      3. 19.3 Capillary Exchange
      4. 19.4 Homeostatic Regulation of the Vascular System
      5. 19.5 Circulatory Pathways
      6. 19.6 Development of Blood Vessels and Fetal Circulation
    4. 20. The Lymphatic and Immune System
      1. 20.1 Anatomy of the Lymphatic and Immune Systems
      2. 20.2 Barrier Defences and the Innate Immune Response
      3. 20.3 The Adaptive Immune Response: T Lymphocytes and Their Functional Types
      4. 20.4 The Adaptive Immune Response: B Lymphocytes and Antibodies
  7. Part 5. Energy, Maintenance, and Environmental Exchange
    1. 21. The Respiratory System
      1. 21.1 Organs and Structures of the Respiratory System
      2. 21.2 The Lungs
      3. 21.3 The Process of Breathing
      4. 21.4 Gas Exchange
      5. 21.5 Transport of Gases
    2. 22. The Digestive System
      1. 22.1 Overview of the Digestive System
      2. 22.2 Digestive System Processes and Regulation
      3. 22.3 The Mouth, Pharynx, and Esophagus
      4. 22.4 The Stomach
      5. 22.5 The Small and Large Intestines
      6. 22.6 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder
      7. 22.7 Chemical Digestion and Absorption: A Closer Look
    3. 23. Metabolism and Nutrition
      1. 23.1 Overview of Metabolic Reactions
      2. 23.2 Carbohydrate Metabolism
      3. 23.3 Lipid Metabolism
      4. 23.4 Protein Metabolism
      5. 23.5 Metabolic States of the Body
      6. 23.6 Energy and Heat Balance
      7. 23.7 Nutrition and Diet
    4. 24. The Urinary System
      1. 24.1 Physical Characteristics of Urine
      2. 24.2 Gross Anatomy of Urine Transport
      3. 24.3 Gross Anatomy of the Kidney
      4. 24.4 Microscopic Anatomy of the Kidney
      5. 24.5 Physiology of Urine Formation
      6. 24.6 Tubular Reabsorption
      7. 24.7 Regulation of Renal Blood Flow
      8. 24.8 Endocrine Regulation of Kidney Function
      9. 24.9 The Urinary System and Homeostasis
    5. 25. Fluid, Electrolyte, and Acid-Base Balance
      1. 25.1 Body Fluids and Fluid Compartments
      2. 25.2 Water Balance
      3. 25.3 Electrolyte Balance
      4. 25.4 Acid-Base Balance
      5. 25.5 Disorders of Acid-Base Balance
  8. Part 6. Human Development and the Continuity of Life
    1. 26. The Reproductive System
      1. 26.1 Anatomy and Physiology of the Testicular Reproductive System
      2. 26.2 Anatomy and Physiology of the Ovarian Reproductive System
    2. 27. Development and Inheritance
      1. 27.1 Fertilization
      2. 27.2 Embryonic Development
      3. 27.3 Fetal Development
      4. 27.4 Changes During Pregnancy, Labour, and Birth
      5. 27.5 Adjustments of the Infant at Birth and Postnatal Stages
      6. 27.6 Lactation
  9. Glossary
  10. Figure Descriptions

Glossary

abdominal aorta:
Portion of the aorta inferior to the aortic hiatus and superior to the common iliac arteries.
abdominopelvic cavity:
Division of the anterior (ventral) cavity that houses the abdominal and pelvic viscera.
abducens nerve:
Sixth cranial nerve; responsible for contraction of one of the extraocular muscles.
abduction:
Movement in the coronal plane that moves a limb laterally away from the body; spreading of the fingers.
abductor:
Moves the bone away from the midline.
ABO blood group:
Blood-type classification based on the presence or absence of A and B glycoproteins on the erythrocyte membrane surface.
absolute refractory period:
Time during an action period when another action potential cannot be generated because the voltage-gated Na+ channel is inactivated.
absorption:
Passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals.
absorptive state:
Also called the fed state; the metabolic state occurring during the first few hours after ingesting food in which the body is digesting food and absorbing the nutrients.
accessory digestive organ:
Includes teeth, tongue, salivary glands, gallbladder, liver, and pancreas.
accessory duct (also duct of Santorini):
Duct that runs from the pancreas into the duodenum.
acetabulum:
Large, cup-shaped cavity located on the lateral side of the hip bone; formed by the junction of the ilium, pubis, and ischium portions of the hip bone.
acetylcholine (ACh):
Neurotransmitter that binds at a motor end-plate to trigger depolarization.
acetyl coenzyme A (acetyl CoA):
Starting molecule of the Krebs cycle.
acid:
Compound that releases hydrogen ions (H+) in solution.
acinus:
Cluster of glandular epithelial cells in the pancreas that secretes pancreatic juice in the pancreas.
acromegaly:
Disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet.
acromial (lateral) end of the clavicle:
Lateral end of the clavicle that articulates with the acromion of the scapula.
acromion (acromial process):
Flattened bony process that extends laterally from the scapular spine to form the bony tip of the shoulder.
acrosomal reaction:
Release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization.
acrosome:
Cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte.
actin:
Protein that makes up most of the thin myofilaments in a sarcomere muscle fibre.
action potential:
Change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibres.
activation energy:
Amount of energy greater than the energy contained in the reactants, which must be overcome for a reaction to proceed.
activation gate:
Part of the voltage-gated Na+ channel that opens when the membrane voltage reaches threshold.
active immunity:
Immunity developed from an individual’s own immune system.
active transport:
Form of transport across the cell membrane that requires input of cellular energy.
acute inflammation:
Inflammation occurring for a limited time period; rapidly developing.
adaptive immune response:
Relatively slow but very specific and effective immune response controlled by lymphocytes.
adduction:
Movement in the coronal plane that moves a limb medially toward or across the midline of the body; bringing fingers together.
adductor:
Moves the bone toward the midline.
adductor brevis:
Muscle that adducts and medially rotates the thigh.
adductor longus:
Muscle that adducts, medially rotates, and flexes the thigh.
adductor magnus:
Muscle with an anterior fascicle that adducts, medially rotates, and flexes the thigh and a posterior fascicle that assists in thigh extension.
adenosine triphosphate (ATP):
Nucleotide containing ribose, an adenine base, and three phosphates; essential in energy transfer.
adenylyl cyclase:
Membrane-bound enzyme that converts ATP to cyclic AMP, creating cAMP, as a result of G-protein activation.
adherens junction:
Type of cell junction; uses adhesion proteins found in either desmosomes or hemidesmosomes, depending on whether they are linking to other cells or the matrix.
adipocytes:
Lipid storage cells.
adipose tissue:
Specialized areolar tissue rich in stored fat.
adrenal artery:
Branch of the abdominal aorta; supplies blood to the adrenal (suprarenal) glands.
adrenal cortex:
Outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produces mineralocorticoids and glucocorticoids.
adrenal glands:
Endocrine glands located at the top of each kidney that are important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels.
adrenal medulla:
Inner layer of the adrenal glands that plays an important role in the stress response by producing epinephrine and norepinephrine.
adrenal vein:
Drains the adrenal or suprarenal glands that are immediately superior to the kidneys; the right adrenal vein enters the inferior vena cava directly, and the left adrenal vein enters the left renal vein.
adrenergic:
Synapse where norepinephrine is released, which binds to α- or β-adrenergic receptors.
adrenocorticotropic hormone (ACTH):
Anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones (also called corticotropin).
aerobic respiration:
Production of ATP in the presence of oxygen.
afferent arterioles:
Branches of high-pressure capillaries bringing blood to the glomerulus.
afferent branch:
Component of a reflex arc that represents the input from a sensory neuron, for either a special or general sense.
afferent lymphatic vessels:
Vessels that lead into a lymph node.
afterbirth:
Third stage of childbirth in which the placenta and associated fetal membranes are expelled.
afterload:
Force the ventricles must develop to effectively pump blood against the resistance in the vessels.
agglutination:
Clustering of cells into masses linked by antibodies.
agonist (also prime mover):
Muscle whose contraction is responsible for producing a particular motion.
agranular leukocytes:
Leukocytes with few granules in their cytoplasm; specifically, monocytes, lymphocytes, and NK cells.
ala (plural = alae):
Small, flaring structure of a nostril that forms the lateral side of the nares.
alar cartilage:
Cartilage that supports the apex of the nose and helps shape the nares; it is connected to the septal cartilage and connective tissue of the alae.
alarm reaction:
The short-term stress, or fight-or-flight, response of stage one of the general adaptation syndrome mediated by the hormones epinephrine and norepinephrine.
albumin:
Most abundant plasma protein, accounting for most of the osmotic pressure of plasma.
aldosterone:
Hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure.
alimentary canal:
Continuous muscular digestive tube that extends from the mouth to the anus.
alkaloid:
Substance, usually from a plant source, that is chemically basic with respect to pH and will stimulate bitter receptors.
allantois:
Fingerlike outpocketing of yolk sac that forms the primitive excretory duct of the embryo; precursor to the urinary bladder.
alpha (α)-adrenergic receptor:
One of the receptors to which epinephrine and norepinephrine bind, which comes in two subtypes: α1 and α2.
alpha cell:
Pancreatic islet cell type that produces the hormone glucagon.
α-dextrin:
Breakdown product of starch.
α-dextrinase:
Brush border enzyme that acts on α-dextrins.
alveolar dead space:
Air space within alveoli that are unable to participate in gas exchange.
alveolar duct:
Small tube that leads from the terminal bronchiole to the respiratory bronchiole and is the point of attachment for alveoli.
alveolar macrophage:
Immune system cell of the alveolus that removes debris and pathogens.
alveolar pore:
Opening that allows airflow between neighbouring alveoli.
alveolar process of the mandible:
Upper border of the mandibular body that contains the lower teeth.
alveolar sac:
Cluster of alveoli.
alveoli (of the breast):
Milk-secreting cells in the mammary gland.
alveolus:
Small, grape-like sac that performs gas exchange in the lungs.
amacrine cell:
Type of cell in the retina that connects to the bipolar cells near the outer synaptic layer and provides the basis for early image processing within the retina.
amino acid:
Building block of proteins; characterized by an amino functional group, carboxyl functional groups, and a variable side chain.
aminopeptidase:
Brush border enzyme that acts on proteins.
amnion:
Transparent membranous sac that encloses the developing fetus and fills with amniotic fluid.
amniotic cavity:
Cavity that opens up between the inner cell mass and the trophoblast; develops into amnion.
amniotic fluid:
Filtrate of maternal plasma and urine.
amphiarthrosis:
Slightly mobile joint.
amphipathic:
Describes a molecule that exhibits a difference in polarity between its two ends, resulting in a difference in water solubility.
ampulla:
In the ear, the structure at the base of a semicircular canal that contains the hair cells and cupula for transduction of rotational movement of the head.
ampulla (of the uterine tube):
Middle portion of the uterine tube in which fertilization often occurs.
amygdala:
Nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional behaviour.
anabolic hormones:
Hormones that stimulate the synthesis of new, larger molecules.
anabolic reactions:
Reactions that build smaller molecules into larger molecules.
anabolism:
Assembly of more complex molecules from simpler molecules.
anaerobic metabolism:
Process during periods of reduced oxygen when pyruvic acid is converted to lactic acid, which may contribute to muscle fatigue.
anal canal:
Final segment of the large intestine.
anal column:
Long fold of mucosa in the anal canal.
anal sinus:
Recess between anal columns.
anaphase:
Third stage of mitosis (and meiosis), during which sister chromatids separate into two new nuclear regions of a dividing cell.
anaphylactic shock:
Type of shock that follows a severe allergic reaction and results from massive vasodilation.
anastomosis (plural = anastomoses):
Area where vessels unite to allow blood to circulate even if there may be partial blockage in another branch.
anatomical dead space:
Air space present in the airway that never reaches the alveoli and therefore never participates in gas exchange.
anatomical neck:
Line on the humerus located around the outside margin of the humeral head.
anatomical position:
Standard reference position used for describing locations and directions on the human body.
anatomical sphincter:
Smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted.
anatomy:
Science that studies the form and composition of the body’s structures.
anchoring junction:
Mechanically attaches adjacent cells to each other or to the basement membrane.
anconeus:
Small muscle on the lateral posterior elbow that extends the forearm.
angiotensin I:
Protein produced by the enzymatic action of renin on angiotensinogen; inactive precursor of angiotensin II.
angiotensin II:
Protein produced by the enzymatic action of ACE on inactive angiotensin I; actively causes vasoconstriction and stimulates aldosterone release by the adrenal cortex.
angiotensin-converting enzyme (ACE):
Enzyme produced by the lungs that catalyzes the reaction of inactive angiotensin I into active angiotensin II.
angiotensinogen:
Inactive protein in the circulation produced by the liver; precursor of angiotensin I; must be modified by the enzymes renin and ACE to be activated.
angle of the rib:
Portion of a rib with the greatest curvature; together, the rib angles form the most posterior extent of the thoracic cage.
anion:
Atom with a negative charge.
ankle joint:
Joint that separates the leg and foot portions of the lower limb; formed by the articulations between the talus bone of the foot inferiorly, and the distal end of the tibia, medial malleolus of the tibia, and lateral malleolus of the fibula superiorly.
annular ligament:
Intrinsic ligament of the elbow articular capsule that surrounds and supports the head of the radius at the proximal radioulnar joint.
antagonist:
Muscle that opposes the action of an agonist.
anterior:
Describes the front or direction toward the front of the body; also referred to as ventral.
anterior arch:
Anterior portion of the ringlike C1 (atlas) vertebra.
anterior border of the tibia:
Narrow, anterior margin of the tibia that extends inferiorly from the tibial tuberosity.
anterior cardiac veins:
Vessels that parallel the small cardiac arteries and drain the anterior surface of the right ventricle, bypass the coronary sinus, and drain directly into the right atrium.
anterior cavity:
Larger body cavity located anterior to the posterior (dorsal) body cavity; includes the serous membrane–lined pleural cavities for the lungs, pericardial cavity for the heart, and peritoneal cavity for the abdominal and pelvic organs; also referred to as ventral cavity.
anterior column:
White matter between the anterior horns of the spinal cord composed of many different groups of axons of both ascending and descending tracts.
anterior corticospinal tract:
Division of the corticospinal pathway that travels through the ventral (anterior) column of the spinal cord and controls axial musculature through the medial motor neurons in the ventral (anterior) horn.
anterior cruciate ligament:
Intracapsular ligament of the knee; extends from anterior, superior surface of the tibia to the inner aspect of the lateral condyle of the femur; resists hyperextension of knee.
anterior horn:
Grey matter of the spinal cord containing multipolar motor neurons, sometimes referred to as the ventral horn.
anterior interventricular artery (also left anterior descending artery or LAD):
Major branch of the left coronary artery that follows the anterior interventricular sulcus.
anterior interventricular sulcus:
Sulcus located between the left and right ventricles on the anterior surface of the heart.
anterior median fissure:
Deep midline feature of the anterior spinal cord, marking the separation between the right and left sides of the cord.
anterior pituitary (adenohypophysis):
Produces two classes of regulatory hormones: releasing hormones, which stimulate the secretion of specific hormones from the anterior pituitary, and inhibiting hormones, which suppress their secretion.
anterior tibial artery:
Branches from the popliteal artery; supplies blood to the anterior tibial region; becomes the dorsalis pedis artery.
antibodies (also immunoglobulins or gamma globulins):
Antigen-specific proteins produced by specialized B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses.
antibody:
Antigen-specific protein secreted by plasma cells; immunoglobulin.
anticoagulant:
Substance such as heparin that opposes coagulation.
anticodon:
Consecutive sequence of three nucleotides on a tRNA molecule that is complementary to a specific codon on an mRNA molecule.
antidiuretic hormone (ADH):
Also known as vasopressin, a hormone that increases the volume of water reabsorbed from the collecting tubules of the kidney.
antigen:
Substance that the body does not recognize as belonging to the “self” and that therefore triggers a defensive response from the leukocytes of the immune system.
antigenic determinant (also epitope):
One of the chemical groups recognized by a single type of lymphocyte antigen receptor.
antigen presentation:
Binding of processed antigen to the protein-binding cleft of a major histocompatibility complex molecule.
antigen processing:
Internalization and digestion of antigen in an antigen-presenting cell.
antigen receptor:
Two-chain receptor by which lymphocytes recognize antigen.
antiporters:
Secondary active transporters that transport substances in opposite directions.
antrum:
Fluid-filled chamber that characterizes a mature tertiary (antral) follicle.
anulus fibrosus:
Tough, fibrous outer portion of an intervertebral disc, which is strongly anchored to the bodies of the adjacent vertebrae.
anuria:
Absence of urine produced; production of 50 mL or less per day.
aorta:
Largest artery in the body, originating from the left ventricle and descending to the abdominal region, where it bifurcates into the common iliac arteries at the level of the fourth lumbar vertebra; arteries originating from the aorta distribute blood to virtually all tissues of the body.
aortic arch:
Arch that connects the ascending aorta to the descending aorta; ends at the intervertebral disk between the fourth and fifth thoracic vertebrae.
aortic hiatus:
Opening in the diaphragm that allows passage of the thoracic aorta into the abdominal region, where it becomes the abdominal aorta.
aortic sinuses:
Small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis.
aortic valve (also aortic semilunar valve):
Valve located at the base of the aorta.
apex (nose):
Tip of the external nose.
apex (sacrum):
The inferior tip of the sacrum.
apneustic centre:
Network of neurons within the pons that stimulate the neurons in the dorsal respiratory group; controls the depth of inspiration.
apocrine secretion:
Release of a substance along with the apical portion of the cell.
apocrine sweat gland:
Type of sweat gland that is associated with hair follicles in the armpits and genital regions.
aponeurosis:
Broad, tendonlike sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone.
apoptosis:
Programmed cell death.
appendicular:
Of the arms and legs.
appendicular skeleton:
All bones of the upper and lower limbs, plus the girdle bones that attach each limb to the axial skeleton.
appendix (vermiform appendix):
Coiled tube attached to the cecum.
aquaporin:
Protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH.
aqueous humour:
Watery fluid that fills the anterior chamber containing the cornea, iris, ciliary body, and lens of the eye.
arachnoid mater:
Middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater.
areola:
Highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling.
areolar tissue (also loose connective tissue):
A type of connective tissue proper that shows little specialization with cells dispersed in the matrix.
arm:
Region of the upper limb located between the shoulder and elbow joints; contains the humerus bone.
arrector pili:
Smooth muscle that is activated in response to external stimuli that pull on hair follicles and make the hair “stand up.”
arteriole (also resistance vessel):
Very small artery that leads to a capillary.
arteriovenous anastomosis:
Short vessel connecting an arteriole directly to a venule and bypassing the capillary beds.
artery:
Blood vessel that conducts blood away from the heart; may be a conducting or distributing vessel.
articular capsule:
Connective tissue structure that encloses the joint cavity of a synovial joint.
articular cartilage:
Thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber.
articular disc:
Meniscus; a fibrocartilage structure found between the bones of some synovial joints; provides padding or smooths movements between the bones; strongly unites the bones together.
articulation:
Where two bone surfaces meet.
ascending aorta:
Initial portion of the aorta, rising from the left ventricle for a distance of approximately 5 cm.
ascending colon:
First region of the colon.
ascending pathway:
Fibre structure that relays sensory information from the periphery through the spinal cord and brain stem to other structures of the brain.
ascending tract:
Central nervous system fibres carrying sensory information from the spinal cord or periphery to the brain.
association area:
Region of cortex connected to a primary sensory cortical area that further processes the information to generate more complex sensory perceptions.
astrocyte:
Star-shaped cell in the central nervous system that regulates ions and uptake and/or breakdown of some neurotransmitters and contributes to the formation of the blood-brain barrier.
atlantoaxial joint:
Series of three articulations between the atlas (C1) vertebra and the axis (C2) vertebra, consisting of the joints between the inferior articular processes of C1 and the superior articular processes of C2, and the articulation between the dens of C2 and the anterior arch of C1.
atlanto-occipital joint:
Articulation between the occipital condyles of the skull and the superior articular processes of the atlas (C1 vertebra).
atlas:
First cervical (C1) vertebra.
atmospheric pressure:
Amount of force exerted by gases in the air surrounding any given surface.
atom:
Smallest unit of an element that retains the unique properties of that element.
atomic number:
Number of protons in the nucleus of an atom.
atoms and molecules:
The smallest unit of any pure substance (element) is an atom; molecules are the chemical building blocks of all body structures.
ATPase:
Enzyme that hydrolyzes ATP to ADP.
ATP synthase:
Protein pore complex that creates ATP.
atrial natriuretic peptide (ANP):
Peptide hormone produced by the walls of the atria in response to high blood pressure, blood volume, or blood sodium that reduces the reabsorption of sodium and water in the kidneys and promotes vasodilation.
atrial reflex (also called Bainbridge reflex):
Autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases.
atrioventricular (AV) node:
Clump of myocardial cells located in the inferior portion of the right atrium within the atrioventricular septum; receives the impulse from the SA node, pauses, and then transmits it into specialized conducting cells within the interventricular septum.
atrioventricular bundle (also bundle of His):
Group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches.
atrioventricular bundle branches (also left or right bundle branches):
Specialized myocardial conductile cells that arise from the bifurcation of the atrioventricular bundle and pass through the interventricular septum; lead to the Purkinje fibres and also to the right papillary muscle via the moderator band.
atrioventricular septum:
Cardiac septum located between the atria and ventricles; atrioventricular valves are located here.
atrioventricular valves (AV valves):
One-way valves located between the atria and ventricles; the valve on the right is called the tricuspid valve, and the one on the left is the mitral or bicuspid valve.
atrium (plural = atria):
Upper or receiving chamber of the heart that pumps blood into the lower chambers just prior to their contraction; the right atrium receives blood from the systemic circuit that flows into the right ventricle; the left atrium receives blood from the pulmonary circuit that flows into the left ventricle.
audition:
Sense of hearing.
auricle (ear):
Fleshy external structure of the ear.
auricle (heart):
Extension of an atrium visible on the superior surface of the heart.
autocrine:
Chemical signal that elicits a response in the same cell that secreted it.
autolysis:
Breakdown of cells by their own enzymatic action.
autonomic ganglia:
Related to the autonomic nervous system, which is divided into the sympathetic and parasympathetic nervous systems.
autonomic nervous system (ANS):
Functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue.
autonomic tone:
Tendency of an organ system to be governed by one division of the autonomic nervous system over the other, such as heart rate being lowered by parasympathetic input at rest.
autophagy:
Lysosomal breakdown of a cell’s own components.
autorhythmicity:
Ability of cardiac muscle to initiate its own electrical impulse that triggers the mechanical contraction that pumps blood at a fixed pace without nervous or endocrine control.
axial:
Of the trunk and head.
axial skeleton:
Central, vertical axis of the body, including the skull, vertebral column, and thoracic cage.
axillary artery:
Continuation of the subclavian artery as it penetrates the body wall and enters the axillary region; supplies blood to the region near the head of the humerus (humeral circumflex arteries); the majority of the vessel continues into the brachium and becomes the brachial artery.
axillary nerve:
Systemic nerve of the arm that arises from the brachial plexus.
axillary vein:
Major vein in the axillary region; drains the upper limb and becomes the subclavian vein.
axis:
Second cervical (C2) vertebra.
axon:
Single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell.
axon hillock:
Tapering of the neuron cell body that gives rise to the axon.
axon segment:
Single stretch of the axon insulated by myelin and bounded by nodes of Ranvier at either end (except for the first, which is after the initial segment, and the last, which is followed by the axon terminal).
axon terminal:
End of the axon, where there are usually several branches extending toward the target cell.
axoplasm:
Cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body.
azygos vein:
Originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region; leads to the superior vena cava.
bacterial flora:
Bacteria in the large intestine.
Bainbridge reflex (also called atrial reflex):
Autonomic reflex that responds to stretch receptors in the atria that send impulses to the cardioaccelerator area to increase HR when venous flow into the atria increases.
ball-and-socket joint:
Synovial joint formed between the spherical end of one bone (the ball) that fits into the depression of a second bone (the socket); found at the hip and shoulder joints; functionally classified as a multiaxial joint.
baroreceptor:
Mechanoreceptor that senses the stretch of blood vessels to indicate changes in blood pressure.
baroreceptor reflex:
Autonomic reflex in which the cardiac centres monitor signals from the baroreceptor stretch receptors and regulate heart function based on blood flow.
barrier defences:
Antipathogen defences deriving from a barrier that physically prevents pathogens from entering the body to establish an infection.
Bartholin’s glands (also greater vestibular glands):
Glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands.
basal cell:
Type of stem cell found in the stratum basale and in the hair matrix that continually undergoes cell division, producing the keratinocytes of the epidermis.
basal lamina:
Thin extracellular layer that lies underneath epithelial cells and separates them from other tissues.
basal metabolic rate (BMR):
Amount of energy expended by the body at rest.
basal nuclei:
Nuclei of the cerebrum (with a few components in the upper brain stem and diencephalon) that are responsible for assessing cortical movement commands and comparing them with the general state of the individual through broad modulatory activity of dopamine neurons; largely related to motor function.
base:
Compound that accepts hydrogen ions (H+) in solution.
basement membrane:
In epithelial tissue, a thin layer of fibrous material that anchors the epithelial tissue to the underlying connective tissue; made up of the basal lamina and reticular lamina.
base of the metatarsal bone:
Expanded, proximal end of each metatarsal bone.
basilar membrane:
In the ear, the floor of the cochlear duct on which the organ of Corti sits.
basophils:
Granulocytes that stain with a basic (alkaline) stain and store histamine and heparin.
B cells:
Lymphocytes that act by differentiating into an antibody-secreting plasma cell.
belly:
Bulky central body of a muscle.
beta (β)-adrenergic receptor:
One of the receptors to which epinephrine and norepinephrine bind, which comes in three subtypes: β1, β2, and β3.
beta (β)-oxidation:
Fatty acid oxidation.
beta cell:
Pancreatic islet cell type that produces the hormone insulin.
Betz cells:
Output cells of the primary motor cortex that cause musculature to move through synapses on cranial and spinal motor neurons.
bi:
Two.
biaxial joint:
Type of diarthrosis; a joint that allows for movements within two planes (two axes).
biceps brachii:
Two-headed muscle that crosses the shoulder and elbow joints to flex the forearm while assisting in supinating it and flexing the arm at the shoulder.
biceps femoris:
Hamstring muscle.
bicuspid valve (also mitral valve or left atrioventricular valve):
Valve located between the left atrium and ventricle; consists of two flaps of tissue.
bile:
Alkaline solution produced by the liver and important for the emulsification of lipids.
bile canaliculus:
Small duct between hepatocytes that collects bile.
bile salts:
Salts that are released from the liver in response to lipid ingestion and surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids.
bilirubin:
Yellowish bile pigment produced when iron is removed from heme and is further broken down into waste products.
biliverdin:
Green bile pigment produced when the noniron portion of heme is degraded into a waste product; converted to bilirubin in the liver.
binocular vision:
Indications of the distance of visual stimuli on the basis of slight differences in the images projected onto either retina.
biogenic amine:
Class of neurotransmitters that are enzymatically derived from amino acids but no longer contain a carboxyl group.
biosynthesis reactions:
Reactions that create new molecules, also called anabolic reactions.
bipennate:
Pennate muscle that has fascicles that are located on both sides of the tendon.
bipolar:
Shape of a neuron with two processes extending from the neuron cell body—the axon and one dendrite.
bipolar cell:
Cell type in the retina that connects the photoreceptors to the RGCs.
blastocoel:
Fluid-filled cavity of the blastocyst.
blastocyst:
Term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta.
blastomere:
Daughter cell of a cleavage.
blood:
Liquid connective tissue composed of formed elements—erythrocytes, leukocytes, and platelets—and a fluid extracellular matrix called plasma; component of the cardiovascular system.
blood-brain barrier (BBB):
Physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS.
blood colloidal osmotic pressure (BCOP):
Pressure exerted by colloids suspended in blood within a vessel; a primary determinant is the presence of plasma proteins.
blood flow:
Movement of blood through a vessel, tissue, or organ that is usually expressed in terms of volume per unit of time.
blood hydrostatic pressure:
Force blood exerts against the walls of a blood vessel or heart chamber.
blood pressure:
Force exerted by the blood against the wall of a vessel or heart chamber; can be described with the more generic term hydrostatic pressure.
blood-testis barrier:
Tight junctions between Sertoli cells that prevent blood-borne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm.
B lymphocytes (also B cells):
Lymphocytes that defend the body against specific pathogens and thereby provide specific immunity.
body:
Midportion of the stomach.
body of the rib:
Shaft portion of a rib.
body of uterus:
Middle section of the uterus.
Bohr effect:
Relationship between blood pH and oxygen dissociation from hemoglobin.
bolus:
Mass of chewed food.
bond:
Electrical force linking atoms.
bone (osseous tissue):
Hard, dense connective tissue that forms the structural elements of the skeleton.
bone marrow:
Tissue found inside bones; the site of all blood cell differentiation and maturation of B lymphocytes.
bony pelvis:
The entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx.
Bowman’s (glomerular) capsule:
Cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialized cells called podocytes (visceral surface) that participate in the filtration process; receives the filtrate, which then passes on to the PCTs.
Boyle’s law:
Relationship between volume and pressure as described by the formula P1V1 = P2V2.
brachial artery:
Continuation of the axillary artery in the brachium; supplies blood to much of the brachial region; gives off several smaller branches that provide blood to the posterior surface of the arm in the region of the elbow; bifurcates into the radial and ulnar arteries at the coronoid fossa.
brachialis:
Muscle deep to the biceps brachii that provides power in flexing the forearm.
brachial plexus:
Nerve plexus associated with the lower cervical spinal nerves and the first thoracic spinal nerve.
brachial vein:
A deep vein that flows into the axillary vein in the brachium formed by joining of the radial vein with the ulnar vein.
brachiocephalic artery:
Single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of the thoracic region.
brachiocephalic vein:
One of a pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins lead to it; drains the upper thoracic region and flows into the superior vena cava.
brachioradialis:
Muscle that can flex the forearm quickly or help lift a load slowly.
brain:
The large organ of the central nervous system composed of white and grey matter, contained within the cranium, and continuous with the spinal cord.
brain case:
Portion of the skull that contains and protects the brain, consisting of the eight bones that form the cranial base and rounded upper skull.
brain stem:
Region of the adult brain that includes the midbrain, pons, and medulla oblongata and develops from the mesencephalon, metencephalon, and myelencephalon of the embryonic brain.
Braxton Hicks contractions:
Weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent.
brevis:
Short.
bridge:
Portion of the external nose that lies in the area of the nasal bones.
broad ligament:
Wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall.
Broca’s area:
Region of the frontal lobe associated with the motor commands necessary for speech production and located only in the cerebral hemisphere responsible for language production, which is the left side in approximately 95 percent of the population.
bronchial artery:
Systemic branch from the aorta that provides oxygenated blood to the lungs in addition to the pulmonary circuit.
bronchial tree:
Collective name for the multiple branches of the bronchi and bronchioles of the respiratory system.
bronchial vein:
Drains the systemic circulation from the lungs and leads to the azygos vein.
bronchiole:
Branch of bronchi that are 1 mm or less in diameter and terminate at alveolar sacs.
bronchoconstriction:
Decrease in the size of the bronchiole due to relaxation of the muscular wall.
bronchodilation:
Increase in the size of the bronchiole due to contraction of the muscular wall.
bronchus:
Tube connected to the trachea that branches into many subsidiaries and provides a passageway for air to enter and leave the lungs.
bronchus-associated lymphoid tissue (BALT):
Lymphoid nodule associated with the respiratory tract.
brown adipose tissue:
Highly vascularized fat tissue packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat.
bruise:
Localized bleeding under the skin due to damaged blood vessels.
brush border:
Formed by microvilli on the surface of certain cuboidal cells; in the kidney, it is found in the PCT; increases surface area for absorption in the kidney.
buccinator:
Muscle that compresses the cheek.
buffer:
Solution containing a weak acid or a weak base that opposes wide fluctuations in the pH of body fluids.
buffy coat:
Thin, pale layer of leukocytes and platelets that separates the erythrocytes from the plasma in a sample of centrifuged blood.
bulbourethral glands (also Cowper’s glands):
Glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation.
bulbous (Ruffini) corpuscles:
Responsible for the detection of stretching of the skin, known as type II cutaneous mechanoreceptors.
bundle of His (also atrioventricular bundle):
Group of specialized myocardial conductile cells that transmit the impulse from the AV node through the interventricular septum; form the left and right atrioventricular bundle branches.
bursa:
Connective tissue sac containing lubricating fluid that prevents friction between adjacent structures, such as skin and bone, tendons and bone, or two muscles.
calcaneal tendon (also Achilles tendon):
Strong tendon that inserts into the calcaneal bone of the ankle.
calcaneus:
Heel bone; posterior, inferior tarsal bone that forms the heel of the foot.
calcitonin:
Peptide hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland that functions to decrease blood calcium levels.
calmodulin:
Regulatory protein that facilitates contraction in smooth muscles.
calorie:
Amount of heat it takes to raise 1 kg (1,000 g) of water by 1°C.
calvaria (also skullcap):
Rounded top of the skull.
calyces:
Cup-like structures receiving urine from the collecting ducts, where it passes on to the renal pelvis and ureter.
canaliculi (singular = canaliculus):
Channels within the bone matrix that house one of an osteocyte’s many cytoplasmic extensions that it uses to communicate and receive nutrients.
capacitance:
Ability of a vein to distend and store blood.
capacitance vessels:
Veins; more distensible than arteries.
capacitation:
Process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers.
capillary:
Smallest of blood vessels where physical exchange occurs between the blood and tissue cells surrounded by interstitial fluid.
capillary bed:
Network of 10–100 capillaries connecting arterioles to venules.
capillary hydrostatic pressure (CHP):
Force blood exerts against a capillary.
capitulum:
Knoblike bony structure located anteriorly on the lateral, distal end of the humerus.
carbaminohemoglobin:
Compound of carbon dioxide and hemoglobin and one of the ways in which carbon dioxide is carried in the blood.
carbohydrate:
Class of organic compounds built from sugar molecules containing carbon, hydrogen, and oxygen in a 1-2-1 ratio.
carbonic anhydrase (CA):
Enzyme that catalyzes the reaction that causes carbon dioxide and water to form carbonic acid.
cardia (also cardiac region):
Part of the stomach surrounding the cardiac orifice (esophageal hiatus).
cardiac accelerator nerves:
Preganglionic sympathetic fibres that cause the heart rate to increase when the cardiovascular centre in the medulla initiates a signal.
cardiac cycle:
Period of time between the onset of atrial contraction (atrial systole) and ventricular relaxation (ventricular diastole).
cardiac muscle:
Striated muscle found in the heart; joined to one another at intercalated discs and under the regulation of pacemaker cells, which contract as one unit to pump blood through the circulatory system. Cardiac muscle is under involuntary control.
cardiac notch:
Depression in the medial surface of the inferior lobe of the left lung where the apex of the heart is located.
cardiac output (CO):
Amount of blood pumped by each ventricle in 1 minute; equals HR multiplied by SV.
cardiac plexus:
Paired complex network of nerve fibres near the base of the heart that receive sympathetic and parasympathetic stimulations to regulate HR.
cardiac reflexes:
Series of autonomic reflexes that enable the cardiovascular centres to regulate heart function based on sensory information from a variety of visceral sensors.
cardiac reserve:
Difference between maximum and resting CO.
cardiac skeleton (also skeleton of the heart):
Reinforced connective tissue located within the atrioventricular septum; includes four rings that surround the openings between the atria and ventricles and the openings to the pulmonary trunk and aorta; the point of attachment for the heart valves.
cardioaccelerator centres:
Stimulate cardiac function by regulating heart rate and stroke volume via sympathetic stimulation from the cardiac accelerator nerve.
cardiogenic shock:
Type of shock that results from the inability of the heart to maintain cardiac output.
cardioinhibitor centres:
Slow cardiac function by decreasing heart rate and stroke volume via parasympathetic stimulation from the vagus nerve.
cardiomyocyte:
Muscle cell of the heart.
cardiovascular centre:
Region in the medulla that controls the cardiovascular system through cardiac accelerator nerves and vasomotor nerves, which are components of the sympathetic division of the autonomic nervous system.
carotid sinuses:
Small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis.
carpal bones:
Eight small bones that form the wrist and base of the hand; these are grouped as a proximal row consisting of (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones, and a distal row containing (from lateral to medial) the trapezium, trapezoid, capitate, and hamate bones.
carpal tunnel:
Passageway between the anterior forearm and hand formed by the carpal bones and flexor retinaculum.
cartilage:
Semirigid connective tissue found on the skeleton in areas where flexibility and smooth surfaces support movement.
cartilaginous joint:
Joint at which the bones are united by hyaline cartilage (synchondrosis) or fibrocartilage (symphysis).
catabolic hormones:
Hormones that stimulate the breakdown of larger molecules.
catabolic reactions:
Reactions that break down larger molecules into their constituent parts.
catabolism:
Breaking down of more complex molecules into simpler molecules.
catalyst:
Substance that increases the rate of a chemical reaction without itself being changed in the process.
cation:
Atom with a positive charge.
cauda equina:
Bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail.
caudal:
Describes a position below or lower than another part of the body proper, near or toward the tail (in humans, the coccyx, or lowest part of the spinal column); also referred to as inferior.
cecum:
Pouch forming the beginning of the large intestine.
celiac ganglion:
One of the collateral ganglia of the sympathetic system that projects to the digestive system.
celiac trunk (also celiac artery):
Major branch of the abdominal aorta; gives rise to the left gastric artery, the splenic artery, and the common hepatic artery that forms the hepatic artery to the liver, the right gastric artery to the stomach, and the cystic artery to the gall bladder.
cell:
Smallest independently functioning unit of all organisms; in animals, a cell contains cytoplasm, composed of fluid and organelles.
cell cycle:
Life cycle of a single cell, from its birth until its division into two new daughter cells.
cell junction:
Point of cell-to-cell contact that connects one cell to another in a tissue.
cell membrane:
Membrane surrounding all animal cells, composed of a lipid bilayer interspersed with various molecules; also known as plasma membrane.
cellular respiration:
Production of ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation.
cementum:
Bone-like tissue covering the root of a tooth.
central canal (Haversian canal):
Longitudinal channel in the centre of each osteon; contains blood vessels, nerves, and lymphatic vessels.
central chemoreceptor:
One of the specialized receptors located in the brain that senses changes in hydrogen ion, oxygen, or carbon dioxide concentrations in the brain.
central nervous system (CNS):
Anatomical division of the nervous system located within the cranial and vertebral cavities, namely, the brain and spinal cord.
central neuron:
The cell body of a neuron in the autonomic system that is located in the central nervous system, specifically the lateral horn of the spinal cord or a brain stem nucleus.
central sulcus:
Surface landmark of the cerebral cortex that marks the boundary between the frontal and parietal lobes.
central tolerance:
B cell tolerance induced in immature B cells of the bone marrow.
central vein:
Vein that receives blood from hepatic sinusoids.
centriole:
Small, self-replicating organelle that provides the origin for microtubule growth and moves DNA during cell division.
centromere:
Region of attachment for two sister chromatids.
centrosome:
Cellular structure that organizes microtubules during cell division.
cephalic phase (also reflex phase):
Initial phase of gastric secretion that occurs before food enters the stomach.
cephalic vein:
Superficial vessel in the upper arm; leads to the axillary vein.
cerebellum:
Region of the adult brain connected primarily to the pons, which developed from the metencephalon (along with the pons), and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord.
cerebral aqueduct:
Connection of the ventricular system between the third and fourth ventricles located in the midbrain.
cerebral cortex:
Outermost layer of grey matter in the brain, where conscious perception takes place.
cerebral hemisphere:
One-half of the bilaterally symmetrical cerebrum.
cerebral peduncles:
Segments of the descending motor pathway that make up the white matter of the ventral midbrain.
cerebrospinal fluid (CSF):
Circulates throughout and around the CNS; it is produced in special structures to perfuse through the nervous tissue of the CNS to remove metabolic wastes from the interstitial fluids of nervous tissues and return them to the bloodstream.
cerebrovascular accident (CVA):
Blockage of blood flow to the brain; also called a stroke.
cerebrum:
Region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness.
cervical curve:
Posteriorly concave curvature of the cervical vertebral column region; a secondary curve of the vertebral column.
cervical plexus:
Nerve plexus associated with the upper cervical spinal nerves.
cervical vertebrae:
Seven vertebrae numbered C1–C7 that are located in the neck region of the vertebral column.
cervix:
Elongate inferior end of the uterus where it connects to the vagina.
channel protein:
Membrane-spanning protein that has an inner pore that allows the passage of one or more substances.
chemical digestion:
Enzymatic breakdown of food.
chemical energy:
Form of energy that is absorbed as chemical bonds form, stored as they are maintained, and released as they are broken.
chemical synapse:
Connection between two neurons, or between a neuron and its target, where a neurotransmitter diffuses across a very short distance.
chemokine:
Soluble, long-range, cell-to-cell communication molecule.
chemoreceptor:
Sensory receptor cell that is sensitive to chemical stimuli, such as in taste, smell, or pain.
chief cell:
Gastric gland cell that secretes pepsinogen.
chloride shift:
Facilitated diffusion that exchanges bicarbonate (HCO3−) with chloride (Cl−) ions.
cholecystokinin (CCK):
Hormone that stimulates the release of pancreatic lipase and the contraction of the gallbladder to release bile salts.
cholinergic:
Synapse at which acetylcholine is released and binds to the nicotinic or muscarinic receptor.
cholinergic system:
Neurotransmitter system of acetylcholine, which includes its receptors and the enzyme acetylcholinesterase.
chondrocytes:
Cells of the cartilage.
chordae tendineae:
String-like extensions of tough connective tissue that extend from the flaps of the atrioventricular valves to the papillary muscles.
chorion:
Membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi.
chorionic membrane:
Precursor to the chorion; forms from extraembryonic mesoderm cells.
chorionic villi:
Projections of the chorionic membrane that burrow into the endometrium and develop into the placenta.
choroid:
Highly vascular tissue in the wall of the eye that supplies the outer retina with blood.
choroid plexus:
Specialized structure containing ependymal cells lining blood capillaries that filter blood to produce CSF in the four ventricles of the brain.
chromaffin:
Neuroendocrine cells of the adrenal medulla that release epinephrine and norepinephrine into the bloodstream as part of sympathetic system activity.
chromatin:
Substance consisting of DNA and associated proteins.
chromosome:
Condensed version of chromatin.
chronic inflammation:
Inflammation occurring for long periods of time.
chyle:
Lipid-rich lymph inside the lymphatic capillaries of the small intestine.
chylomicron:
Large lipid-transport compound made up of triglycerides, phospholipids, cholesterol, and proteins.
chylomicrons:
Vesicles containing cholesterol and triglycerides that transport lipids out of the intestinal cells and into the lymphatic and circulatory systems.
chyme:
Soupy liquid created when food is mixed with digestive juices.
chymotrypsin:
Pancreatic enzyme that digests protein.
chymotrypsinogen:
Proenzyme that is activated by trypsin into chymotrypsin.
cilia:
Small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface.
ciliary body:
Smooth muscle structure on the interior surface of the iris that controls the shape of the lens through the zonule fibres.
ciliated columnar epithelium:
Tissue composed of simple columnar epithelial cells with cilia on their apical surfaces.
circadian rhythm:
Internal perception of the daily cycle of light and dark based on retinal activity related to sunlight.
circle of Willis:
Unique anatomical arrangement of blood vessels around the base of the brain that maintains perfusion of blood into the brain, even if one component of the structure is blocked or narrowed.
circular (also sphincter):
Fascicles that are concentrically arranged around an opening.
circular fold (also plica circulare):
Deep fold in the mucosa and submucosa of the small intestine.
circulatory shock:
Also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism.
circumduction:
Circular motion of the arm, thigh, hand, thumb, or finger that is produced by the sequential combination of flexion, abduction, extension, and adduction.
circumflex artery:
Branch of the left coronary artery that follows the coronary sulcus.
cisterna chyli:
Bag-like vessel that forms the beginning of the thoracic duct.
citric acid cycle:
Also called the Krebs cycle or the tricarboxylic acid cycle; converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules.
class II MHC:
Molecules expressed only on the cells of the immune system, specifically cells that affect other arms of the immune response.
class switching:
Ability of B cells to change the class of antibody they produce without altering the specificity for antigen.
clavicle:
Collarbone; elongated bone that articulates with the manubrium of the sternum medially and the acromion of the scapula laterally.
clavicular notch:
Paired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the clavicle.
cleavage:
Form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells.
cleavage furrow:
Contractile ring that forms around a cell during cytokinesis and pinches the cell into two halves.
clitoris (also glans clitoris):
Nerve-rich area of the vulva that contributes to sexual sensation during intercourse.
clonal anergy:
Process whereby B cells that react to soluble antigens in bone marrow are made nonfunctional.
clonal deletion:
Removal of self-reactive B cells by inducing apoptosis.
clonal expansion:
Growth of a clone of selected lymphocytes.
clonal selection:
Stimulating growth of lymphocytes that have specific receptors.
clone:
Group of lymphocytes sharing the same antigen receptor.
closed reduction:
Manual manipulation of a broken bone to set it into its natural position without surgery.
clotting factors:
Group of 12 identified substances active in coagulation.
coagulation:
Formation of a blood clot; part of the process of hemostasis.
coccyx:
Small bone located at the inferior end of the adult vertebral column that is formed by the fusion of four coccygeal vertebrae; also referred to as the tailbone.
cochlea:
Auditory portion of the inner ear containing structures to transduce sound stimuli.
cochlear duct:
Space within the auditory portion of the inner ear that contains the organ of Corti and is adjacent to the scala tympani and scala vestibuli on either side.
codon:
Consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid.
collagen fibre:
Flexible fibrous proteins that give connective tissue tensile strength.
collateral ganglia:
Ganglia outside of the sympathetic chain that are targets of sympathetic preganglionic fibres, which are the celiac, inferior mesenteric, and superior mesenteric ganglia.
colloid:
Liquid mixture in which the solute particles consist of clumps of molecules large enough to scatter light.
colon:
Part of the large intestine between the cecum and the rectum.
colony-stimulating factors (CSFs):
Glycoproteins that trigger the proliferation and differentiation of myeloblasts into granular leukocytes (basophils, neutrophils, and eosinophils).
colostrum:
Thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins.
common bile duct:
Structure formed by the union of the common hepatic duct and the gallbladder’s cystic duct.
common carotid artery:
Blood vessel that branches off the aorta (or the brachiocephalic artery on the right) and supplies blood to the head and neck.
common hepatic artery:
Branch of the celiac trunk that forms the hepatic artery, the right gastric artery, and the cystic artery.
common hepatic duct:
Duct formed by the merger of the two hepatic ducts.
common iliac artery:
Branch of the aorta that leads to the internal and external iliac arteries.
common iliac vein:
One of a pair of veins that flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; divides into external and internal iliac veins near the inferior portion of the sacroiliac joint.
common pathway:
Final coagulation pathway activated by either the intrinsic or the extrinsic pathway and ending in the formation of a blood clot.
compact bone:
Dense osseous tissue that can withstand compressive forces.
complement:
Enzymatic cascade of constitutive blood proteins that have antipathogen effects, including the direct killing of bacteria.
compliance:
Degree to which a blood vessel can stretch as opposed to being rigid.
compound:
Substance composed of two or more different elements joined by chemical bonds.
concentration gradient:
Difference in the concentration of a substance between two regions.
concentric contraction:
Muscle contraction that shortens the muscle to move a load.
conceptus:
Preimplantation stage of a fertilized egg and its associated membranes.
conducting zone:
Region of the respiratory system that includes the organs and structures that provide passageways for air and are not directly involved in gas exchange.
conduction:
Transfer of heat through physical contact.
condylar process of the mandible:
Thickened upward projection from the posterior margin of the mandibular ramus.
condyle:
Oval-shaped process located at the top of the condylar process of the mandible.
condyloid joint:
Synovial joint in which the shallow depression at the end of one bone receives a rounded end from a second bone or a rounded structure formed by two bones; found at the metacarpophalangeal joints of the fingers or the radiocarpal joint of the wrist; functionally classified as a biaxial joint.
cone photoreceptor:
One of the two types of retinal receptor cell that is specialized for colour vision through the use of three photopigments distributed through three separate populations of cells.
connective tissue:
Type of tissue that serves to hold in place, connect, and integrate the body’s organs and systems.
connective tissue membrane:
Connective tissue that encapsulates organs and lines movable joints.
connective tissue proper:
Connective tissue containing a viscous matrix, fibres, and cells.
continuous capillary:
Most common type of capillary, found in virtually all tissues except epithelia and cartilage; contains very small gaps in the endothelial lining that permit exchange.
continuous conduction:
Slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na+ channels located along the entire length of the cell membrane.
contractility:
Ability to shorten (contract) forcibly.
contraction phase:
Twitch contraction phase when tension increases.
contralateral:
Word meaning “on the opposite side,” as in axons that cross the midline in a fibre tract.
control centre:
Compares values to their normal range; deviations cause the activation of an effector.
convection:
Transfer of heat between the skin and air or water.
convergent:
Fascicles that extend over a broad area and converge on a common attachment site.
coracoid process:
Short, hooklike process that projects anteriorly and laterally from the superior margin of the scapula.
cornea:
Fibrous covering of the anterior region of the eye that is transparent so that light can pass through it.
corneal reflex:
Protective response to stimulation of the cornea that causes contraction of the orbicularis oculi muscle, resulting in blinking of the eye.
coronal plane:
Two-dimensional, vertical plane that divides the body or organ into anterior and posterior portions; also referred to as frontal plane.
coronal suture:
Joint that unites the frontal bone to the right and left parietal bones across the top of the skull.
corona radiata:
In an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur.
coronary arteries:
Branches of the ascending aorta that supply blood to the heart; the left coronary artery feeds the left side of the heart, the left atrium and ventricle, and the interventricular septum; the right coronary artery feeds the right atrium, portions of both ventricles, and the heart conduction system.
coronary sinus:
Large, thin-walled vein on the posterior surface of the heart that lies within the atrioventricular sulcus and drains the heart myocardium directly into the right atrium.
coronary sulcus:
Sulcus that marks the boundary between the atria and ventricles.
coronary veins:
Vessels that drain the heart and generally parallel the large surface arteries.
coronoid process of the ulna:
Projecting bony lip located on the anterior, proximal ulna; forms the inferior margin of the trochlear notch.
corpus albicans:
Nonfunctional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum.
corpus callosum:
Large white matter structure that connects the right and left cerebral hemispheres.
corpus cavernosum:
Either of two columns of erectile tissue in the penis that fill with blood during an erection.
corpus luteum:
Transformed follicle after ovulation that secretes progesterone.
corpus spongiosum (plural = corpora cavernosa):
Column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis.
cortex:
In hair, the second or middle layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb.
cortical nephrons:
Nephrons with loops of Henle that do not extend into the renal medulla.
cortical reaction:
Following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida, creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy.
corticobulbar tract:
Connection between the cortex and the brain stem responsible for generating movement.
corticospinal tract:
Connection between the cortex and the spinal cord responsible for generating movement.
cortisol:
Glucocorticoid important in gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system.
costal cartilage:
Hyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternum.
costal facet:
Site on the lateral sides of a thoracic vertebra for articulation with the head of a rib.
costal groove:
Shallow groove along the inferior margin of a rib that provides passage for blood vessels and a nerve.
countercurrent multiplier system:
Involves the descending and ascending loops of Henle directing forming urine in opposing directions to create a concentration gradient when combined with variable permeability and sodium pumping.
covalent bond:
Chemical bond in which two atoms share electrons, thereby completing their valence shells.
coxal bone:
Hip bone.
cranial:
Describes a position above or higher than another part of the body proper; also referred to as superior.
cranial cavity:
Division of the posterior (dorsal) cavity that houses the brain.
cranial nerve:
One of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck.
cranial nerve ganglion:
Sensory ganglion of cranial nerves.
craniosacral system:
Alternate name for the parasympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in brain stem nuclei and the lateral horn of the sacral spinal cord; also referred to as craniosacral outflow.
cranium:
Skull.
creatine phosphate:
Phosphagen used to store energy from ATP and transfer it to muscle.
cricoid cartilage:
Portion of the larynx composed of a ring of cartilage with a wide posterior region and a thinner anterior region; attached to the esophagus.
crown:
Portion of tooth visible superior to the gum line.
cuboid:
Tarsal bone that articulates posteriorly with the calcaneus bone, medially with the lateral cuneiform bone, and anteriorly with the fourth and fifth metatarsal bones.
cupula:
Specialized structure within the base of a semicircular canal that bends the stereocilia of hair cells when the head rotates by way of the relative movement of the enclosed fluid.
cuspid (also canine):
Pointed tooth used for tearing and shredding food.
cutaneous membrane:
Skin; epithelial tissue made up of a stratified squamous epithelial cells that cover the outside of the body.
cuticle:
In hair, the outermost layer of keratinocytes originating from the hair matrix, as seen in a cross-section of the hair bulb.
cyclic adenosine monophosphate (cAMP):
Second messenger that, in response to adenylyl cyclase activation, triggers a phosphorylation cascade.
cystic duct:
Duct through which bile drains and enters the gallbladder.
cytokines:
Class of proteins that act as autocrine or paracrine signalling molecules; in the cardiovascular system, they stimulate the proliferation of progenitor cells and help stimulate both nonspecific and specific resistance to disease.
cytokinesis:
Final stage in cell division, where the cytoplasm divides to form two separate daughter cells.
cytoplasm:
Internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles, cellular solutes, and suspended materials.
cytoskeleton:
“skeleton” of a cell; formed by rodlike proteins that support the cell’s shape and provide, among other functions, locomotive abilities.
cytosol:
Clear, semifluid medium of the cytoplasm, made up mostly of water.
cytotoxic T cells (Tc):
T lymphocytes with the ability to induce apoptosis in target cells.
Dalton’s law:
Statement of the principle that a specific gas type in a mixture exerts its own pressure as if that specific gas type was not part of a mixture of gases.
deciduous tooth:
One of 20 “baby teeth.”
decomposition reaction:
Type of catabolic reaction in which one or more bonds within a larger molecule are broken, resulting in the release of smaller molecules or atoms.
deep:
Describes a position farther from the surface of the body.
defecation:
Elimination of undigested substances from the body in the form of feces.
defensins:
Antimicrobial proteins released from neutrophils and macrophages that create openings in the plasma membranes to kill cells.
deglutition:
Three-stage process of swallowing.
dehydration:
State of containing insufficient water in blood and other tissues.
delta cell:
Minor cell type in the pancreas that secretes the hormone somatostatin.
deltoid:
Shoulder muscle that abducts the arm as well as flexes and medially rotates it and extends and laterally rotates it.
deltoid tuberosity:
Roughened, V-shaped region located laterally on the midshaft of the humerus.
denaturation:
Change in the structure of a molecule through physical or chemical means.
dendrite:
One of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells.
dendrites:
Branches off the neuron cell body and appear as thin extensions.
dendritic cells:
Two types of phagocytic cells in the thymus that are derived from monocytes.
dens:
Bony projection (odontoid process) that extends upward from the body of the C2 (axis) vertebra.
dense body:
Sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments.
dense connective tissue:
Connective tissue proper that contains many fibres that provide both elasticity and protection.
dentes:
Teeth.
dentin:
Bone-like tissue immediately deep to the enamel of the crown or cementum of the root of a tooth.
dentition:
Set of teeth.
deoxyhemoglobin:
Molecule of hemoglobin without an oxygen molecule bound to it.
deoxyribonuclease:
Pancreatic enzyme that digests DNA.
deoxyribonucleic acid (DNA):
Deoxyribose-containing nucleotide that stores genetic information.
depolarization:
Change in a cell membrane potential from rest toward zero.
depolarize:
Process where the membrane potential of muscle fibre becomes less negative (closer to zero).
depression:
Downward (inferior) motion of the scapula or mandible.
dermal papilla (plural = dermal papillae):
Extension of the papillary layer of the dermis that increases surface contact between the epidermis and dermis.
dermis:
Layer of skin between the epidermis and hypodermis, composed mainly of connective tissue and containing blood vessels, hair follicles, sweat glands, and other structures.
descending aorta:
Portion of the aorta that continues downward past the end of the aortic arch; subdivided into the thoracic aorta and the abdominal aorta.
descending colon:
Part of the colon between the transverse colon and the sigmoid colon.
descending tract:
Central nervous system fibres carrying motor commands from the brain to the spinal cord or periphery.
desmosome:
Type of cell junction that anchors cells together by linking adhesion molecules across their membranes.
detrusor muscle:
Smooth muscle in the bladder wall; fibres run in all directions to reduce the size of the organ when emptying it of urine.
development:
Changes an organism goes through during its life.
diapedesis (also emigration):
Process by which leukocytes squeeze through adjacent cells in a blood vessel wall to enter tissues.
diaphragm:
Skeletal muscle that separates the thoracic and abdominal cavities and is dome-shaped at rest.
diaphysis:
Tubular shaft that runs between the proximal and distal ends of a long bone.
diarthrosis:
Freely mobile joint.
diastole:
Period of time when the heart muscle is relaxed and the chambers fill with blood.
diastolic pressure:
Lower number recorded when measuring arterial blood pressure; represents the minimal value corresponding to the pressure that remains during ventricular relaxation.
diencephalon:
Region of the adult brain that retains its name from embryonic development and includes the thalamus and hypothalamus.
differentiation:
Process in which a cell may undertake major changes in its size, shape, metabolic activity, and overall function.
diffusion:
Movement of a substance from an area of higher concentration to one of lower concentration.
digastric:
Muscle that has anterior and posterior bellies and elevates the hyoid bone and larynx when one swallows; it also depresses the mandible.
digital veins:
Drain the digits and feed into the palmar arches of the hand and dorsal venous arch of the foot.
dihydroxyvitamin D (calcitriol):
Active form of vitamin D required by the intestinal epithelial cells for the absorption of calcium.
dilation:
First stage of childbirth, involving an increase in cervical diameter.
dipeptidase:
Brush border enzyme that acts on proteins.
diploid:
Condition marked by the presence of a double complement of genetic material (two sets of chromosomes, one set inherited from each of two parents).
direct pathway:
Connections within the basal nuclei from the striatum to the globus pallidus internal segment and substantia nigra pars reticulata that disinhibit the thalamus to increase cortical control of movement.
disaccharide:
Pair of carbohydrate monomers bonded by dehydration synthesis via a glycosidic bond.
distal:
Describes a position farther from the point of attachment or the trunk of the body.
distal convoluted tubules (DCT):
Portions of the nephron distal to the loop of Henle that receive hyposmotic filtrate from the loop of Henle and empty into collecting ducts.
diuresis:
Excess production of urine.
diuretic:
Compound that increases urine output, leading to decreased water conservation.
DNA polymerase:
Enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication.
DNA replication:
Process of duplicating a molecule of DNA.
dorsal:
Describes the back or direction toward the back of the body; also referred to as posterior.
dorsal (posterior) root ganglion:
Sensory ganglion attached to the posterior nerve root of a spinal nerve.
dorsal cavity:
Posterior body cavity that houses the brain and spinal cord; also referred to as the posterior body cavity.
dorsal column system:
Ascending tract of the spinal cord associated with fine touch and proprioceptive sensations.
dorsal respiratory group (DRG):
Region of the medulla oblongata that stimulates the contraction of the diaphragm and intercostal muscles to induce inspiration.
dorsal stream:
Connections between cortical areas from the occipital to parietal lobes that are responsible for the perception of visual motion and guiding movement of the body in relation to that motion.
dorsiflexion:
Movement at the ankle that brings the top of the foot toward the anterior leg.
dorsum nasi:
Intermediate portion of the external nose that connects the bridge to the apex and is supported by the nasal bone.
double helix:
Characteristic of DNA where two strands attach via hydrogen bonds between the bases of the component nucleotides.
downregulation:
Decrease in the number of hormone receptors, typically in response to chronically excessive levels of a hormone.
ductus arteriosus:
Shunt in the fetal pulmonary trunk that diverts oxygenated blood back to the aorta.
ductus deferens (also vas deferens):
Duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred to as the vas deferens.
ductus venosus:
Shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava.
duodenal gland (also Brunner’s gland):
Mucous-secreting gland in the duodenal submucosa.
duodenum:
First part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum.
dural sinus:
Any of the venous structures surrounding the brain, enclosed within the dura mater, which drain blood from the CNS to the common venous return of the jugular veins.
dura mater:
Tough, fibrous, outer layer of the meninges that is attached to the inner surface of the cranium and vertebral column and surrounds the entire CNS.
ear ossicles:
Three small bones located in the middle ear cavity that serve to transmit sound vibrations to the inner ear.
eccentric contraction:
Muscle contraction that lengthens the muscle as the tension is diminished.
eccrine sweat gland:
Type of sweat gland that is common throughout the skin surface; it produces a hypotonic sweat for thermoregulation.
ectoderm:
Primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails.
ectopic pregnancy:
Implantation of an embryo outside of the uterus.
effector:
Organ that can cause a change in a value.
effector protein:
Enzyme that catalyzes the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor.
effector T cells:
Immune cells with a direct, adverse effect on a pathogen.
efferent arteriole:
Arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of Henle; portion of the portal system.
efferent branch:
Component of a reflex arc that represents the output, with the target being an effector, such as muscle or glandular tissue.
efferent lymphatic vessels:
Vessels that lead out of a lymph node.
effort:
Force applied to the handle of a lever.
ejaculatory duct:
Duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra.
ejection fraction:
Portion of the blood that is pumped or ejected from the heart with each contraction; mathematically represented by SV divided by EDV.
elastic artery (also conducting artery):
Artery with abundant elastic fibres located closer to the heart, which maintains the pressure gradient and conducts blood to smaller branches.
elastic cartilage:
Type of cartilage, with elastin as the major protein, characterized by rigid support as well as elasticity.
elastic fibre:
Fibrous protein within connective tissue that contains a high percentage of the protein elastin, which allows the fibres to stretch and return to their original size.
elasticity:
Ability to stretch and rebound.
elbow joint:
Joint located between the upper arm and forearm regions of the upper limb; formed by the articulations between the trochlea of the humerus and the trochlear notch of the ulna, and the capitulum of the humerus and the head of the radius.
electrical gradient:
Difference in the electrical charge (potential) between two regions.
electrical synapse:
Connection between two neurons, or any two electrically active cells, where ions flow directly through channels spanning their adjacent cell membranes.
electrocardiogram (ECG):
Surface recording of the electrical activity of the heart that can be used for diagnosis of irregular heart function; also abbreviated as EKG.
electron:
Subatomic particle having a negative charge and nearly no mass; found orbiting the atom’s nucleus.
electron shell:
Area of space a given distance from an atom’s nucleus in which electrons are grouped.
electron transport chain (ETC):
ATP production pathway in which electrons are passed through a series of oxidation-reduction reactions that forms water and produces a proton gradient.
element:
Substance that cannot be created or broken down by ordinary chemical means.
elevation:
Upward (superior) motion of the scapula or mandible.
embryo:
Developing human during weeks 3–8.
embryonic disc:
Composed of embryonic cells and the amniotic cavity.
embryonic folding:
Process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder.
emigration (also diapedesis):
Process by which leukocytes squeeze through adjacent cells in a blood vessel wall to enter tissues.
enamel:
Covering of the dentin of the crown of a tooth.
encapsulated corpuscle ending:
Configuration of a sensory receptor neuron with dendrites surrounded by specialized structures to aid in transduction of a particular type of sensation, such as the lamellated corpuscles in the deep dermis and subcutaneous tissue.
end diastolic volume (EDV; also preload):
The amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction.
endocardium:
Innermost layer of the heart lining the heart chambers and heart valves; composed of endothelium reinforced with a thin layer of connective tissue that binds to the myocardium.
endochondral ossification:
Process in which bone forms by replacing hyaline cartilage.
endocrine gland:
Tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion.
endocrine system:
Cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes.
endocytosis:
Import of material into the cell by formation of a membrane-bound vesicle.
endoderm:
Innermost embryonic germ layer from which most of the digestive system and lower respiratory system derive.
endogenous:
Describes a substance made in the human body.
endometrium:
Inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses.
endomysium:
Loose, well-hydrated connective tissue covering each muscle fibre in a skeletal muscle.
endoneurium:
Innermost layer of connective tissue that surrounds individual axons within a nerve.
endoplasmic reticulum (ER):
Cellular organelle that consists of interconnected membrane-bound tubules, which may or may not be associated with ribosomes (rough type or smooth type, respectively).
endosteum:
Delicate membranous lining of a bone’s medullary cavity.
endothelins:
Group of vasoconstrictive, 21-amino acid peptides; produced by endothelial cells of the renal blood vessels, mesangial cells, and cells of the DCT.
endothelium:
Layer of smooth, simple squamous epithelium that lines the endocardium and blood vessels.
end systolic volume (ESV):
Amount of blood remaining in each ventricle following systole.
energy-consuming phase:
First phase of glycolysis, in which two molecules of ATP are necessary to start the reaction.
energy-yielding phase:
Second phase of glycolysis, during which energy is produced.
enteric nervous system (ENS):
Neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections.
enteric plexus:
Neuronal plexus in the wall of the intestines, which is part of the enteric nervous system.
enteroendocrine cell:
Gastric gland cell that releases hormones.
enterohepatic circulation:
Recycling mechanism that conserves bile salts.
enterokinase:
Enzyme located in the wall of the small intestine that activates trypsin.
enteropeptidase (enterokinase):
Intestinal brush border enzyme that activates trypsinogen to trypsin.
enzyme:
Protein or RNA that catalyzes chemical reactions.
eosinophils:
Granulocytes that stain with eosin; they release antihistamines and are especially active against parasitic worms.
ependymal cell:
Glial cell type in the CNS responsible for producing cerebrospinal fluid.
epicardial coronary arteries:
Surface arteries of the heart that generally follow the sulci.
epicardium:
Innermost layer of the serous pericardium and the outermost layer of the heart wall.
epidermis:
Outermost tissue layer of the skin.
epididymis (plural = epididymides):
Coiled tubular structure in which sperm start to mature and are stored until ejaculation.
epiglottis:
Leaf-shaped piece of elastic cartilage that is a portion of the larynx that swings to close the trachea during swallowing.
epimysium:
Outer layer of connective tissue around a skeletal muscle.
epinephrine:
Primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline.
epineurium:
Outermost layer of connective tissue that surrounds an entire nerve.
epiphyseal line:
Completely ossified remnant of the epiphyseal plate.
epiphyseal plate (also growth plate):
Sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length.
epiphysis:
Wide section at each end of a long bone; filled with spongy bone and red marrow.
epiploic appendage:
Small sac of fat-filled visceral peritoneum attached to teniae coli.
epithalamus:
Region of the diencephalon containing the pineal gland.
epithelial membrane:
Epithelium attached to a layer of connective tissue.
epithelial tissue:
Type of tissue that serves primarily as a covering or lining of body parts, protecting the body; it also functions in absorption, transport, and secretion.
equilibrium:
Sense of balance that includes sensations of position and movement of the head.
erectile tissue:
Located in the shaft of the penis and composed of three column-like chambers.
erector spinae group:
Large muscle mass of the back; primary extensor of the vertebral column.
erythrocyte (also red blood cell):
Mature myeloid blood cell that is composed mostly of hemoglobin and functions primarily in the transportation of oxygen and carbon dioxide.
erythropoietin (EPO):
Glycoprotein that triggers the bone marrow to produce RBCs; secreted by the kidney in response to low oxygen levels.
esophageal plexus:
Neuronal plexus in the wall of the esophagus that is part of the enteric nervous system.
esophagus:
Muscular tube that runs from the pharynx to the stomach.
estrogens:
Class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy.
ethmoid air cell:
One of several small, air-filled spaces located within the lateral sides of the ethmoid bone, between the orbit and upper nasal cavity.
ethmoid bone:
Unpaired bone that forms the roof and upper lateral walls of the nasal cavity, portions of the floor of the anterior cranial fossa and the medial wall of the orbit, and the upper portion of the nasal septum.
Eustachian tube:
Tube connecting the pharynx with the middle ear, which helps equilibrate air pressure across the tympanic membrane; it is normally closed but will pop open when the muscles of the pharynx contract during swallowing or yawning.
evaporation:
Transfer of heat that occurs when water changes from a liquid to a gas.
eversion:
Foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned laterally, away from the midline.
exchange reaction:
Type of chemical reaction in which bonds are both formed and broken, resulting in the transfer of components.
excitability:
Ability to undergo neural stimulation.
excitable membrane:
Cell membrane that regulates the movement of ions so that an electrical signal can be generated.
excitation-contraction coupling:
Sequence of events from motor neuron signalling to a skeletal muscle fibre to contraction of the fibre’s sarcomeres.
excitatory postsynaptic potential (EPSP):
Graded potential in the postsynaptic membrane that is the result of depolarization and makes an action potential more likely to occur.
executive functions:
Cognitive processes of the prefrontal cortex that lead to directing goal-directed behaviour, which is a precursor to executing motor commands.
exocrine gland:
Group of epithelial cells that secrete substances through ducts that open to the skin or to internal body surfaces that lead to the exterior of the body.
exocrine system:
Cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts.
exocytosis:
Export of a substance out of a cell by formation of a membrane-bound vesicle.
exogenous:
Describes a substance made outside of the human body.
expiration (also exhalation):
Process that causes the air to leave the lungs.
expiratory reserve volume (ERV):
Amount of air that can be forcefully exhaled after a normal tidal exhalation.
expulsion:
Second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth.
extensibility:
Ability to lengthen (extend).
extension:
Movement in the sagittal plane that increases the angle of a joint (straightens the joint); motion involving posterior bending of the vertebral column or returning to the upright position from a flexed position.
extensor:
Muscle that increases the angle at the joint.
extensor digitorum longus:
Muscle that is lateral to the tibialis anterior.
extensor hallucis longus:
Muscle that is partly deep to the tibialis anterior and extensor digitorum longus.
extensor radialis longus:
Muscle that extends and abducts the hand at the wrist.
external acoustic meatus:
Ear canal opening located on the lateral side of the skull.
external anal sphincter:
Voluntary skeletal muscle sphincter in the anal canal.
external callus:
Collar of hyaline cartilage and bone that forms around the outside of a fracture.
external carotid artery:
Arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx.
external ear:
Structures on the lateral surface of the head, including the auricle and the ear canal up to the tympanic membrane.
external elastic membrane:
Membrane composed of elastic fibres that separates the tunica media from the tunica externa; seen in larger arteries.
external iliac artery:
Branch of the common iliac artery that leaves the body cavity and becomes a femoral artery; supplies blood to the lower limbs.
external iliac vein:
Formed when the femoral vein passes into the body cavity; drains the legs and leads to the common iliac vein.
external intercostal:
Superficial intercostal muscles that raise the rib cage.
external jugular vein:
One of a pair of major veins located in the superficial neck region that drains blood from the more superficial portions of the head, scalp, and cranial regions and leads to the subclavian vein.
external nose:
Region of the nose that is easily visible to others.
external oblique:
Superficial abdominal muscle with fascicles that extend inferiorly and medially.
external occipital protuberance:
Small bump located at the midline on the posterior skull.
external respiration:
Gas exchange that occurs in the alveoli.
external root sheath:
Outer layer of the hair follicle that is an extension of the epidermis, which encloses the hair root.
external urinary (urethral) sphincter:
Skeletal muscle; must be relaxed consciously to void urine.
exteroceptor:
Sensory receptor that is positioned to interpret stimuli from the external environment, such as photoreceptors in the eye or somatosensory receptors in the skin.
extracellular fluid (ECF):
Fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluid found in other reservoirs in the body.
extraocular muscles:
Six skeletal muscles that control eye movement within the orbit.
extrapyramidal system:
Pathways between the brain and spinal cord that are separate from the corticospinal tract and are responsible for modulating the movements generated through that primary pathway.
extrinsic ligament:
Ligament located outside of the articular capsule of a synovial joint.
extrinsic muscles of the hand:
Muscles that move the wrists, hands, and fingers and originate on the arm.
extrinsic pathway:
Initial coagulation pathway that begins with tissue damage and results in the activation of the common pathway.
facet:
Small, flattened area on a bone for an articulation (joint) with another bone, or for muscle attachment.
facial bones:
14 bones that support the facial structures and form the upper and lower jaws and the hard palate.
facial nerve:
Seventh cranial nerve; responsible for contraction of the facial muscles and for part of the sense of taste, as well as causing saliva production.
facilitated diffusion:
Diffusion of a substance with the aid of a membrane protein.
false ribs:
Vertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at all.
fascicle:
Small bundles of nerve or muscle fibres enclosed by connective tissue.
fast glycolytic (FG):
Muscle fibre that primarily uses anaerobic glycolysis.
fast oxidative (FO):
Intermediate muscle fibre that is between slow oxidative and fast glycolytic fibres.
fatty acid oxidation:
Breakdown of fatty acids into smaller-chain fatty acids and acetyl CoA.
fauces:
Portion of the posterior oral cavity that connects the oral cavity to the oropharynx.
Fc region:
In an antibody molecule, the site where the two termini of the heavy chains come together; many cells have receptors for this portion of the antibody, adding functionality to these molecules.
feces:
Semisolid waste product of digestion.
femoral artery:
Continuation of the external iliac artery after it passes through the body cavity; divides into several smaller branches, the lateral deep femoral artery, and the genicular artery; becomes the popliteal artery as it passes posterior to the knee.
femoral nerve:
Systemic nerve of the anterior leg that arises from the lumbar plexus.
femoral vein:
Drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall.
femoropatellar joint:
Portion of the knee joint consisting of the articulation between the distal femur and the patella.
femur:
Thigh bone; the single bone of the thigh.
fenestrated capillary:
Type of capillary with pores or fenestrations in the endothelium that allow for rapid passage of certain small materials.
fenestrations:
Small windows through a cell allowing rapid filtration based on size; formed in such a way as to allow substances to cross through a cell without mixing with cell contents.
ferritin:
Protein-containing storage form of iron found in the bone marrow, liver, and spleen.
fertilization:
Unification of genetic material from male and female haploid gametes.
fertilization membrane:
Impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy.
fetus:
Developing human during the time from the end of the embryonic period (week 9) to birth.
fibrin:
Insoluble, filamentous protein that forms the structure of a blood clot.
fibrinogen:
Plasma protein produced in the liver and involved in blood clotting.
fibrinolysis:
Gradual degradation of a blood clot.
fibroblast:
Most abundant cell type in connective tissue, secretes protein fibres and matrix into the extracellular space.
fibrocartilage:
Tough form of cartilage, made of thick bundles of collagen fibres embedded in chondroitin sulfate ground substance.
fibrocyte:
Less active form of fibroblast.
fibroelastic membrane:
Specialized membrane that connects the ends of the C-shape cartilage in the trachea; contains smooth muscle fibres.
fibrous joint:
Joint where the articulating areas of the adjacent bones are connected by fibrous connective tissue.
fibrous pericardium:
Sturdy outer layer made of tough, dense connective tissue that protects the heart and maintains its position in the thorax.
fibrous tunic:
Outer layer of the eye primarily composed of connective tissue known as the sclera and cornea.
fibula:
Thin, non-weight-bearing bone found on the lateral side of the leg.
fibular collateral ligament:
The second extrinsic ligaments of the knee.
fibularis brevis (also peroneus brevis):
Muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints.
fibularis longus (also peroneus longus):
Muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints.
fibular nerve:
Systemic nerve of the posterior leg that begins as part of the sciatic nerve.
fibular notch:
Wide groove on the lateral side of the distal tibia for articulation with the fibula at the distal tibiofibular joint.
fight-or-flight response:
Set of responses induced by sympathetic activity that lead to either fleeing a threat or standing up to it, which in the modern world is often associated with anxious feelings.
filling time:
Duration of ventricular diastole during which filling occurs.
filtration:
In the cardiovascular system, the movement of material from a capillary into the interstitial fluid, moving from an area of higher pressure to lower pressure.
filtration slits:
Formed by pedicels of podocytes; substances filter between the pedicels based on size.
fimbriae:
Fingerlike projections on the distal uterine tubes.
first messenger:
Hormone that binds to a cell membrane hormone receptor and triggers activation of a second messenger system.
fissures:
Separate the lobes of the lungs from each other.
fixator:
Synergist that assists an agonist by preventing or reducing movement at another joint, thereby stabilizing the origin of the agonist.
flagellum:
Appendage on certain cells formed by microtubules and modified for movement.
flat bone:
Thin and curved bone; serves as a point of attachment for muscles and protects internal organs.
flatus:
Gas in the intestine.
flexion:
Movement in the sagittal plane that decreases the angle of a joint (bends the joint); motion involving anterior bending of the vertebral column.
flexor:
Muscle that decreases the angle at the joint.
flexor carpi radialis:
Muscle that flexes and abducts the hand at the wrist.
flexor carpi ulnaris:
Muscle that flexes and adducts the hand at the wrist.
flexor digitorum superficialis:
Muscle that flexes the hand and the digits.
flexor retinaculum:
Strong band of connective tissue at the anterior wrist that spans the top of the U-shaped grouping of the carpal bones to form the roof of the carpal tunnel.
floating ribs:
Vertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another rib.
fluid compartment:
Fluid inside all cells of the body constitutes a compartment system that is largely segregated from other systems.
fluid connective tissue:
Specialized cells that circulate in a watery fluid containing salts, nutrients, and dissolved proteins.
follicle:
Ovarian structure of one oocyte and surrounding granulosa (and later theca) cells.
follicle-stimulating hormone (FSH):
Anterior pituitary hormone that stimulates the production and maturation of sex cells.
follicular phase:
Phase of the ovarian cycle when the tertiary follicles are growing and secreting estrogen.
folliculogenesis:
Development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins.
fontanelle:
Expanded area of fibrous connective tissue that separates the brain case bones of the skull prior to birth and during the first year after birth.
fontanelles:
Expanded areas of fibrous connective tissue that separate the braincase bones of the skull prior to birth and during the first year after birth.
foot:
Portion of the lower limb located distal to the ankle joint.
foramen magnum:
Large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium.
foramen ovale:
Opening in the fetal heart that allows blood to flow directly from the right atrium to the left atrium, bypassing the fetal pulmonary circuit.
forced breathing (also hyperpnea):
Mode of breathing that occurs during exercise or by active thought that requires muscle contraction for both inspiration and expiration.
forearm:
Region of the upper limb located between the elbow and wrist joints; contains the radius and ulna bones.
forebrain:
Anterior region of the adult brain that develops from the prosencephalon and includes the cerebrum and diencephalon.
formed elements:
Cellular components of blood (erythrocytes, leukocytes, and platelets).
forming urine:
Filtrate undergoing modifications through secretion and reabsorption before true urine is produced.
fossa (plural = fossae):
Shallow depression on the surface of a bone.
fossa ovalis:
Oval-shaped depression in the interatrial septum that marks the former location of the foramen ovale.
fourth ventricle:
The portion of the ventricular system that is in the region of the brain stem and opens into the subarachnoid space through the median and lateral apertures.
fovea:
Exact centre of the retina at which visual stimuli are focused for maximal acuity, where the retina is thinnest and there is nothing but photoreceptors.
fovea capitis:
Minor indentation on the head of the femur that serves as the site of attachment for the ligament to the head of the femur.
fracture:
Broken bone.
fracture hematoma:
Blood clot that forms at the site of a broken bone.
Frank-Starling mechanism:
Relationship between ventricular stretch and contraction in which the force of heart contraction is directly proportional to the initial length of the muscle fibre.
free nerve ending:
Configuration of a sensory receptor neuron with dendrites in the connective tissue of the organ, such as in the dermis of the skin, that are most often sensitive to chemical, thermal, and mechanical stimuli.
frontal bone:
Unpaired bone that forms the forehead, roof of the orbit, and floor of the anterior cranial fossa.
frontal eye field:
Region of the frontal lobe associated with motor commands to orient the eyes toward an object of visual attention.
frontalis:
Front part of the occipitofrontalis muscle.
frontal lobe:
Region of the cerebral cortex directly beneath the frontal bone of the cranium.
frontal plane:
Two-dimensional, vertical plane that divides the body or organ into anterior and posterior portions; also referred to as coronal plane.
frontal sinus:
Air-filled space within the frontal bone; most anterior of the paranasal sinuses.
fulcrum:
Fixed point that a force is applied to on the handle of a lever.
functional residual capacity (FRC):
Sum of ERV and RV, which is the amount of air that remains in the lungs after a tidal expiration.
fundus:
Dome-shaped region of the stomach above and to the left of the cardia.
fundus (of the uterus):
Domed portion of the uterus that is superior to the uterine tubes.
fusiform:
Muscle that has fascicles that are spindle-shaped to create large bellies.
G0 phase:
Phase of the cell cycle usually entered from the G1 phase; characterized by long or permanent periods where the cell does not move forward into the DNA synthesis phase.
G1 phase:
First phase of the cell cycle, after a new cell is born.
G2 phase:
Third phase of the cell cycle, after the DNA synthesis phase.
gallbladder:
Accessory digestive organ that stores and concentrates bile.
gamete:
Haploid reproductive cell that contributes genetic material to form an offspring.
ganglion:
Localized collection of neuron cell bodies in the peripheral nervous system.
ganglionic neuron:
Specifically refers to the cell body of a neuron in the autonomic system that is located in a ganglion.
gap junction:
Channels between adjacent cardiac muscle fibres that allow the depolarizing current produced by cations to flow from one cardiac muscle cell to the next.
gastric emptying:
Process by which mixing waves gradually cause the release of chyme into the duodenum.
gastric gland:
Gland in the stomach mucosal epithelium that produces gastric juice.
gastric juice:
Complex digestive fluid.
gastric lipase:
Secreted by the chief cells in the stomach and responsible for lipid digestion.
gastric phase:
Phase of gastric secretion that begins when food enters the stomach.
gastric pit:
Narrow channel formed by the epithelial lining of the stomach mucosa.
gastric plexuses:
Neuronal networks in the wall of the stomach that are part of the enteric nervous system.
gastrin:
Peptide hormone that stimulates secretion of hydrochloric acid and gut motility.
gastrocnemius:
Most superficial muscle of the calf.
gastrocolic reflex:
Propulsive movement in the colon activated by the presence of food in the stomach.
gastroileal reflex:
Long reflex that increases the strength of segmentation in the ileum.
gastrulation:
Process of cell migration and differentiation into three primary germ layers following cleavage and implantation.
gated:
Property of a channel that determines how it opens under specific conditions, such as voltage change or physical deformation.
G cell:
Gastrin-secreting enteroendocrine cell.
gene:
Functional length of DNA that provides the genetic information necessary to build a protein.
gene expression:
Active interpretation of the information coded in a gene to produce a functional gene product.
general adaptation syndrome (GAS):
The human body’s three-stage response pattern to short- and long-term stress.
general sense:
Any sensory system that is distributed throughout the body and incorporated into organs of multiple other systems, such as the walls of the digestive organs or the skin.
generator potential:
Graded potential from dendrites of a unipolar cell that generates the action potential in the initial segment of that cell’s axon.
genome:
Entire complement of an organism’s DNA; found within virtually every cell.
germinal centres:
Clusters of rapidly proliferating B cells found in secondary lymphoid tissues.
gestation:
In human development, the period required for embryonic and fetal development in utero; pregnancy.
gigantism:
Disorder in children caused when abnormally high levels of GH prompt excessive growth.
gingiva:
Gum.
glabella:
Slight depression of frontal bone, located at the midline between the eyebrows.
gland:
Structure made up of one or more cells modified to synthesize and secrete chemical substances.
glans penis:
Bulbous end of the penis that contains a large number of nerve endings.
glassy membrane:
Layer of connective tissue that surrounds the base of the hair follicle, connecting it to the dermis.
glenohumeral joint:
Shoulder joint; articulation between the glenoid cavity of the scapula and head of the humerus; multiaxial ball-and-socket joint that allows for flexion/extension, abduction/adduction, circumduction, and medial/lateral rotation of the humerus.
glenoid cavity (also glenoid fossa):
Shallow depression located on the lateral scapula, between the superior and lateral borders.
glenoid labrum:
Lip of fibrocartilage located around the outside margin of the glenoid cavity of the scapula.
glial cell:
One of the various types of neural tissue cells responsible for maintenance of the tissue and largely responsible for supporting neurons.
globin:
Heme-containing globular protein that is a constituent of hemoglobin.
globulins:
Heterogeneous group of plasma proteins that includes transport proteins, clotting factors, immune proteins, and others.
glomerular filtration rate (GFR):
Rate of renal filtration.
glomerulus:
Tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size.
glossopharyngeal nerve:
Ninth cranial nerve; responsible for the contraction of muscles in the tongue and throat and for part of the sense of taste as well as causing saliva production.
glottis:
Opening between the vocal folds through which air passes when producing speech.
glucagon:
Pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels.
glucocorticoids:
Hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism.
gluconeogenesis:
Process of glucose synthesis from pyruvate or other molecules.
gluteal group:
Muscle group that extends, flexes, rotates, adducts, and abducts the femur.
gluteal tuberosity:
Roughened area on the posterior side of the proximal femur, extending inferiorly from the base of the greater trochanter.
gluteus maximus:
Largest of the gluteus muscles that extends the femur.
gluteus medius:
Muscle deep to the gluteus maximus that abducts the femur at the hip.
gluteus minimus:
Smallest of the gluteal muscles; deep to the gluteus medius.
glycocalyx:
Coating of sugar molecules that surrounds the cell membrane.
glycogen:
Form that glucose assumes when it is stored.
glycolysis:
Series of metabolic reactions that breaks down glucose into pyruvate and produces ATP.
glycoprotein:
Protein that has one or more carbohydrates attached.
glycosuria:
Presence of glucose in the urine; caused by high blood glucose levels that exceed the ability of the kidneys to reabsorb the glucose; usually the result of untreated or poorly controlled diabetes mellitus.
goblet cell:
Unicellular gland found in columnar epithelium that secretes mucous.
Golgi apparatus:
Cellular organelle formed by a series of flattened, membrane-bound sacs that functions in protein modification, tagging, packaging, and transport.
gomphosis:
Type of fibrous joint in which the root of a tooth is anchored into its bony jaw socket by strong periodontal ligaments.
gonadal artery:
Branch of the abdominal aorta; supplies blood to the gonads or reproductive organs; also described as ovarian arteries or testicular arteries, depending on the sex of the individual.
gonadal vein:
Generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual.
gonadotropin-releasing hormone (GnRH):
Hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland.
gonadotropins:
Hormones that regulate the function of the gonads.
gonads:
Reproductive organs (testes and ovaries) that produce gametes and reproductive hormones.
G protein:
Protein associated with a cell membrane hormone receptor that initiates the next step in a second messenger system upon activation by hormone-receptor binding.
gracilis:
Muscle that adducts the thigh and flexes the leg at the knee.
graded muscle response:
Modification of contraction strength.
graded potential:
Change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it.
granular leukocytes:
Leukocytes with abundant granules in their cytoplasm; specifically, neutrophils, eosinophils, and basophils.
granulosa cells:
Supportive cells in the ovarian follicle that produce estrogen.
granzyme:
Apoptosis-inducing substance contained in granules of NK cells and cytotoxic T cells.
great cardiac vein:
Vessel that follows the interventricular sulcus on the anterior surface of the heart and flows along the coronary sulcus into the coronary sinus on the posterior surface; parallels the anterior interventricular artery and drains the areas supplied by this vessel.
great cerebral vein:
Receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus.
greater curvature:
The convex lateral surface of the stomach.
greater pelvis (also greater pelvic cavity or false pelvis):
Broad space above the pelvic brim defined laterally by the fanlike portion of the upper ilium.
greater sciatic notch:
Large, U-shaped indentation located on the posterior margin of the ilium, superior to the ischial spine.
greater splanchnic nerve:
Nerve that contains fibres of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the celiac ganglion.
greater trochanter:
Large, bony expansion of the femur that projects superiorly from the base of the femoral neck.
greater tubercle:
Enlarged prominence located on the lateral side of the proximal humerus.
great saphenous vein:
Prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and leads to the femoral vein.
grey matter:
Regions of the nervous system containing cell bodies of neurons with few or no myelinated axons; actually may be more pink or tan in colour but called grey in contrast to white matter.
grey rami communicantes (singular = ramus communicans):
Unmyelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the postganglionic sympathetic fibre.
gross anatomy:
Study of the larger structures of the body, typically with the unaided eye; also referred to as macroscopic anatomy.
ground substance:
Fluid or semifluid portion of the matrix.
growth:
Process of increasing in size.
growth hormone (GH):
Anterior pituitary hormone that promotes tissue building and influences nutrient metabolism (also called somatotropin).
gustation:
Sense of taste.
gustatory receptor cells:
Sensory cells in the taste bud that transduce the chemical stimuli of gustation.
gyrus:
Ridge formed by convolutions on the surface of the cerebrum or cerebellum.
hair:
Keratinous filament growing out of the epidermis.
hair bulb:
Structure at the base of the hair root that surrounds the dermal papilla.
hair cells:
Mechanoreceptor cells found in the inner ear that transduce stimuli for the senses of hearing and balance.
hair follicle:
Cavity or sac from which hair originates.
hair follicle plexus:
Follicles are also wrapped in a plexus of nerve endings—detect the movement of hair at the surface of the skin, such as when an insect may be walking along the skin.
hair matrix:
Layer of basal cells from which a strand of hair grows.
hair papilla:
Mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle.
hair root:
Part of hair that is below the epidermis anchored to the follicle.
hair shaft:
Part of hair that is above the epidermis but is not anchored to the follicle.
Haldane effect:
Relationship between the partial pressure of oxygen and the affinity of hemoglobin for carbon dioxide.
hallux:
Big toe; digit 1 of the foot.
hamstring group:
Three long muscles on the back of the leg.
hand:
Region of the upper limb distal to the wrist joint.
haploid:
Contain only half the DNA of a diploid cell; examples are ova and sperm cells.
hard palate:
Bony structure that forms the roof of the mouth and floor of the nasal cavity, formed by the palatine process of the maxillary bones and the horizontal plate of the palatine bones.
haustral contraction:
Slow segmentation in the large intestine.
haustrum:
Small pouch in the colon created by tonic contractions of teniae coli.
head of the femur:
Rounded, proximal end of the femur that articulates with the acetabulum of the hip bone to form the hip joint.
head of the fibula:
Small, knoblike, proximal end of the fibula; articulates with the inferior aspect of the lateral condyle of the tibia.
head of the humerus:
Smooth, rounded region on the medial side of the proximal humerus; articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint.
head of the metatarsal bone:
Expanded, distal end of each metatarsal bone.
head of the radius:
Disc-shaped structure that forms the proximal end of the radius; articulates with the capitulum of the humerus as part of the elbow joint, and with the radial notch of the ulna as part of the proximal radioulnar joint.
head of the rib:
Posterior end of a rib that articulates with the bodies of thoracic vertebrae.
head of the ulna:
Small, rounded distal end of the ulna; articulates with the ulnar notch of the distal radius, forming the distal radioulnar joint.
heart rate (HR):
Number of times the heart contracts (beats) per minute.
heart sounds:
Sounds heard via auscultation with a stethoscope of the closing of the atrioventricular valves (“lub”) and semilunar valves (“dub”).
heavy chain:
Larger protein chain of an antibody.
helper T cells (Th):
T cells that secrete cytokines to enhance other immune responses, involved in activation of both B and T cell lymphocytes.
hematocrit (also packed cell volume):
Volume percentage of erythrocytes in a sample of centrifuged blood.
hematopoiesis:
Production of blood cells, which occurs in the red marrow of the bones.
hematopoietic stem cell:
Type of pluripotent stem cell that gives rise to the formed elements of blood (hemocytoblast).
heme:
Red, iron-containing pigment to which oxygen binds in hemoglobin.
hemidesmosomes:
Type of cell junction that links cells to the extracellular matrix.
hemocytoblast:
Hematopoietic stem cell that gives rise to the formed elements of blood.
hemoglobin:
Oxygen-carrying compound in erythrocytes.
hemolysis:
Destruction (lysis) of erythrocytes and the release of their hemoglobin into circulation.
hemopoiesis:
Production of the formed elements of blood.
hemopoietic growth factors:
Chemical signals including erythropoietin, thrombopoietin, colony-stimulating factors, and interleukins that regulate the differentiation and proliferation of particular blood progenitor cells.
hemorrhage:
Excessive bleeding.
hemosiderin:
Protein-containing storage form of iron found in the bone marrow, liver, and spleen.
hemostasis:
Physiological process by which bleeding ceases.
Henry’s law:
Statement of the principle that the concentration of gas in a liquid is directly proportional to the solubility and partial pressure of that gas.
heparin:
Short-acting anticoagulant stored in mast cells and released when tissues are injured; opposes prothrombin.
hepatic artery:
Artery that supplies oxygenated blood to the liver.
hepatic lobule:
Hexagonal-shaped structure composed of hepatocytes that radiate outward from a central vein.
hepatic portal system:
Specialized circulatory pathway that carries blood from digestive organs to the liver for processing before being sent to the systemic circulation.
hepatic portal vein:
Vein that supplies deoxygenated nutrient-rich blood to the liver.
hepatic sinusoid:
Blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery.
hepatic vein:
Drains systemic blood from the liver and flows into the inferior vena cava.
hepatocytes:
Major functional cells of the liver.
hepatopancreatic ampulla (also ampulla of Vater):
Bulb-like point in the wall of the duodenum where the bile duct and main pancreatic duct unite.
hepatopancreatic sphincter (also sphincter of Oddi):
Sphincter regulating the flow of bile and pancreatic juice into the duodenum.
hilum:
Concave structure on the mediastinal surface of the lungs where blood vessels, lymphatic vessels, nerves, and a bronchus enter the lung.
hindbrain:
Posterior region of the adult brain that develops from the rhombencephalon and includes the pons, medulla oblongata, and cerebellum.
hinge joint:
Synovial joint at which the convex surface of one bone articulates with the concave surface of a second bone; includes the elbow, knee, ankle, and interphalangeal joints; functionally classified as a uniaxial joint.
hip bone:
Coxal bone; one of two paired bones that form the pelvic girdle; each consists of three areas: the ilium, ischium, and pubis.
hip joint:
Joint located at the proximal end of the lower limb; formed by the articulation between the acetabulum of the hip bone and the head of the femur.
hippocampus:
Grey matter deep in the temporal lobe that is very important for long-term memory formation.
histamine:
Vasoactive mediator in granules of mast cells; the primary cause of allergies and anaphylactic shock.
histone:
Family of proteins that associate with DNA in the nucleus to form chromatin.
hole:
Opening or depression in a bone.
holocrine secretion:
Release of a substance caused by the rupture of a gland cell, which becomes part of the secretion.
homeostasis:
Steady state of body systems that living organisms maintain.
homologous:
Describes two copies of the same chromosome (not identical), one inherited from each parent.
hormone:
Secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body.
hormone receptor:
Protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response.
human chorionic gonadotropin (hCG):
Hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo.
humeroulnar joint:
Articulation between the trochlea of humerus and the trochlear notch of the ulna; uniaxial hinge joint that allows for flexion/extension of the forearm.
humerus:
Single bone of the upper arm.
hyaline cartilage:
Most common type of cartilage, smooth and made of short collagen fibres embedded in a chondroitin sulfate ground substance.
hydrochloric acid (HCl):
Digestive acid secreted by parietal cells in the stomach.
hydrogen bond:
Very weak bond between molecules or between parts of large polar molecules like water.
hydrophilic:
Describes a substance or structure attracted to water.
hydrophobic:
Describes a substance or structure repelled by water.
hydrostatic pressure:
Pressure exerted by a fluid against a wall, caused by its own weight or pumping force.
hymen:
Membrane that covers part of the opening of the vagina.
hyoid bone:
Small, U-shaped bone located in the upper neck that does not contact any other bone.
hypercalcemia:
Condition characterized by abnormally high levels of calcium.
hypercapnia:
Abnormally elevated blood levels of CO2.
hyperchloremia:
Higher-than-normal blood chloride levels.
hyperextension:
Excessive extension of a joint, beyond the normal range of movement.
hyperflexion:
Excessive flexion of a joint, beyond the normal range of movement.
hyperkalemia:
Higher-than-normal blood potassium levels.
hypernatremia:
Abnormal increase in blood sodium levels.
hyperparathyroidism:
Disorder caused by overproduction of PTH that results in abnormally elevated blood calcium.
hyperphosphatemia:
Abnormally increased blood phosphate levels.
hyperplasia:
Process in which one cell splits to produce new cells.
hyperpolarization:
Period of the action potential when the membrane voltage is below −70 mV with K+ channels open and potassium ions reach equilibrium.
hypertension:
Chronic and persistent blood pressure measurements of 140/90 mm Hg or above.
hypertonia:
Abnormally high muscle tone.
hypertonic:
Describes a solution concentration that is higher than a reference concentration.
hypertrophic cardiomyopathy:
Pathological enlargement of the heart, generally for no known reason.
hypertrophy:
Addition of structural proteins to muscle fibres.
hypervolemia:
Abnormally high levels of fluid and blood within the body.
hypocalcemia:
Condition characterized by abnormally low levels of calcium.
hypocapnia:
Abnormally low blood levels of CO2.
hypochloremia:
Lower-than-normal blood chloride levels.
hypodermis:
Connective tissue connecting the integument to the underlying bone and muscle.
hypoglossal nerve:
12th cranial nerve; responsible for the contraction of muscles of the tongue.
hypokalemia:
Abnormally decreased blood levels of potassium.
hyponatremia:
Lower-than-normal levels of sodium in the blood.
hyponychium:
Thickened layer of stratum corneum that lies below the free edge of the nail.
hypoparathyroidism:
Disorder caused by underproduction of PTH that results in abnormally low blood calcium.
hypophosphatemia:
Abnormally low blood phosphate levels.
hypophyseal (pituitary) fossa:
Shallow depression on top of the sella turcica that houses the pituitary (hypophyseal) gland.
hypophyseal portal system:
Network of blood vessels that enables hypothalamic hormones to travel into the anterior lobe of the pituitary without entering the systemic circulation.
hypothalamus:
Major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis.
hypotonia:
Abnormally low muscle tone caused by the absence of low-level contractions.
hypotonic:
Describes a solution concentration that is lower than a reference concentration.
hypovolemia:
Abnormally low levels of fluid and blood within the body.
hypovolemic shock:
Type of circulatory shock caused by excessive loss of blood volume due to hemorrhage or possibly dehydration.
hypoxia:
Lack of oxygen supply to the tissues.
IgA:
Antibody whose dimer is secreted by exocrine glands, is especially effective against digestive and respiratory pathogens, and can pass immunity to an infant through breastfeeding.
IgD:
Class of antibody whose only known function is as a receptor on naive B cells; important in B cell activation.
IgE:
Antibody that binds to mast cells and causes antigen-specific degranulation during an allergic response.
IgG:
Main blood antibody of late primary and early secondary responses; passed from carrier to unborn child via placenta.
IgM:
Antibody whose monomer is a surface receptor of naive B cells; the pentamer is the first antibody made during primary responses.
ileocecal sphincter:
Sphincter located where the small intestine joins with the large intestine.
ileum:
End of the small intestine between the jejunum and the large intestine.
iliac crest:
Curved, superior margin of the ilium.
iliac fossa:
Shallow depression found on the anterior and medial surfaces of the upper ilium.
iliacus:
Muscle that, along with the psoas major, makes up the iliopsoas.
iliocostalis cervicis:
Muscle of the iliocostalis group associated with the cervical region.
iliocostalis group:
Laterally placed muscles of the erector spinae.
iliocostalis lumborum:
Muscle of the iliocostalis group associated with the lumbar region.
iliocostalis thoracis:
Muscle of the iliocostalis group associated with the thoracic region.
iliopsoas group:
Muscle group consisting of iliacus and psoas major muscles; flexes the thigh at the hip, rotates it laterally, and flexes the trunk of the body onto the hip.
ilium:
Superior portion of the hip bone.
immune system:
Series of barriers, cells, and soluble mediators that combine in response to infections of the body by pathogenic organisms.
immunoglobulin (Ig, also antibody or gamma globulin):
Antigen-specific proteins produced by specialized B lymphocytes that protect the body by binding to foreign objects such as bacteria and viruses.
immunological memory:
Ability of the adaptive immune response to mount a stronger and faster immune response upon reexposure to a pathogen.
implantation:
When the developing zygote lodges into the uterus for development.
inactivation gate:
Part of a voltage-gated Na+ channel that closes when the membrane potential reaches +30 mV.
inactive proenzymes:
Forms in which proteases are stored and released to prevent the inappropriate digestion of the native proteins of the stomach, pancreas, and small intestine.
incisor:
Midline, chisel-shaped tooth used for cutting into food.
incontinence:
Loss of ability to control micturition.
incus (also anvil):
Ossicle of the middle ear that connects the malleus to the stapes.
indirect pathway:
Connections within the basal nuclei from the striatum through the globus pallidus external segment and subthalamic nucleus to the globus pallidus internal segment/substantia nigra pars compacta that result in inhibition of the thalamus to decrease cortical control of movement.
inferior:
Describes a position below or lower than another part of the body proper, near or toward the tail (in humans, the coccyx, or lowest part of the spinal column); also referred to as caudal.
inferior angle of scapula:
The most inferior portion of the scapula, particularly important because it serves as the attachment point for several powerful muscles involved in shoulder and upper limb movements.
inferior articular process:
Bony process that extends downward from the vertebral arch of a vertebra that articulates with the superior articular process of the next lower vertebra.
inferior colliculus:
Half of the midbrain tectum that is part of the brain stem auditory pathway.
inferior mesenteric ganglion:
One of the collateral ganglia of the sympathetic system that projects to the digestive system.
inferior nasal concha:
One of the paired bones that project from the lateral walls of the nasal cavity to form the largest and most inferior of the nasal conchae.
inferior pubic ramus:
Narrow segment of bone that passes inferiorly and laterally from the pubic body; joins with the ischial ramus to form the ischiopubic ramus.
inferior rotation:
Movement of the scapula during upper limb adduction in which the glenoid cavity of the scapula moves in a downward direction as the medial end of the scapular spine moves in an upward direction.
inferior vena cava:
Large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium.
inflammation:
Basic innate immune response characterized by heat, redness, pain, and swelling.
infrahyoid muscles:
Anterior neck muscles that are attached to, and inferior to, the hyoid bone.
infraspinatus:
Muscle that laterally rotates the arm.
infraspinous fossa:
Broad depression located on the posterior scapula, inferior to the spine.
infundibulum:
Stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk).
ingestion:
Taking food into the GI tract through the mouth.
inguinal canal:
Opening in abdominal wall that connects the testes to the abdominal cavity.
inhibin:
Hormone secreted by the male and female gonads that inhibits FSH production by the anterior pituitary.
inhibiting hormones:
Hormones that inhibit secretion from the anterior pituitary.
inhibitory postsynaptic potential (IPSP):
Graded potential in the postsynaptic membrane that is the result of hyperpolarization and makes an action potential less likely to occur.
initial segment:
First part of the axon as it emerges from the axon hillock, where the electrical signals known as action potentials are generated.
innate immune response:
Rapid but relatively nonspecific immune response.
inner cell mass:
Cluster of cells within the blastocyst that is fated to become the embryo.
inner ear:
Structure within the temporal bone that contains the sensory apparati of hearing and balance.
innermost intercostal:
The deepest intercostal muscles that draw the ribs together.
inner segment:
In the eye, the section of a photoreceptor that contains the nucleus and other major organelles for normal cellular functions.
inorganic compound:
Substance that does not contain both carbon and hydrogen.
insertion:
End of a skeletal muscle that is attached to the structure (usually a bone) that is moved when the muscle contracts.
inspiration (also inhalation):
Process that causes air to enter the lungs.
inspiratory capacity (IC):
Sum of the TV and IRV, which is the amount of air that can maximally be inhaled past a tidal expiration.
inspiratory reserve volume (IRV):
Amount of air that enters the lungs due to deep inhalation past the tidal volume.
insulin:
Pancreatic hormone that enhances the cellular uptake and utilization of glucose, thereby decreasing blood glucose levels.
insulin-like growth factors (IGF):
Protein that enhances cellular proliferation, inhibits apoptosis, and stimulates the cellular uptake of amino acids for protein synthesis.
integral protein:
Membrane-associated protein that spans the entire width of the lipid bilayer.
integration (association areas):
Nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response.
integumentary system:
Skin and its accessory structures.
interatrial septum:
Cardiac septum located between the two atria; contains the fossa ovalis after birth.
intercalated cell:
Specialized cell of the collecting ducts that secrete or absorb acid or bicarbonate; important in acid-base balance.
intercalated disc:
Physical junction between adjacent cardiac muscle cells; consisting of desmosomes, specialized linking proteoglycans, and gap junctions that allow passage of ions between the two cells.
intercondylar eminence:
Irregular elevation on the superior end of the tibia, between the articulating surfaces of the medial and lateral condyles.
intercondylar fossa:
Deep depression on the posterior side of the distal femur that separates the medial and lateral condyles.
intercostal artery:
Branch of the thoracic aorta; supplies blood to the muscles of the thoracic cavity and vertebral column.
intercostal muscles:
Muscles that span the spaces between the ribs.
intercostal nerve:
Systemic nerve in the thoracic cavity that is found between two ribs.
interferons:
Early induced proteins made in virally infected cells that cause nearby cells to make antiviral proteins.
interleukins:
Signalling molecules that may function in hemopoiesis, inflammation, and specific immune responses.
intermediate cuneiform:
Middle of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the medial cuneiform bone, laterally with the lateral cuneiform bone, and anteriorly with the second metatarsal bone.
intermediate filament:
Type of cytoskeletal filament made of keratin, characterized by an intermediate thickness, and playing a role in resisting cellular tension.
internal acoustic meatus:
Opening into the petrous ridge, located on the lateral wall of the posterior cranial fossa.
internal anal sphincter:
Involuntary smooth muscle sphincter in the anal canal.
internal callus:
Fibrocartilaginous matrix, in the endosteal region, between the two ends of a broken bone.
internal capsule:
Segment of the descending motor pathway that passes between the caudate nucleus and the putamen.
internal carotid artery:
Arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with branches of the vertebral artery forming the arterial circle; supplies blood to the brain.
internal elastic membrane:
Membrane composed of elastic fibres that separates the tunica intima from the tunica media; seen in larger arteries.
internal iliac artery:
Branch from the common iliac arteries; supplies blood to the urinary bladder, walls of the pelvis, external genitalia, and the medial portion of the femoral region; in females, also provides blood to the uterus and vagina.
internal iliac vein:
Drains the pelvic organs and integument; formed from several smaller veins in the region; leads to the common iliac vein.
internal intercostal:
Intermediate intercostal muscles that draw the ribs together.
internal jugular vein:
One of a pair of major veins located in the neck region that passes through the jugular foramen and canal and flows parallel to the common carotid artery that is more or less its counterpart; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein.
internal oblique:
Flat, intermediate abdominal muscle with fascicles that run perpendicular to those of the external oblique.
internal respiration:
Gas exchange that occurs at the level of body tissues.
internal root sheath:
Innermost layer of keratinocytes in the hair follicle that surround the hair root up to the hair shaft.
internal thoracic vein (also internal mammary vein):
Drains the anterior surface of the chest wall and leads to the brachiocephalic vein.
internal urinary (urethral) sphincter:
Smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra.
internodal pathways:
Specialized conductile cells within the atria that transmit the impulse from the SA node throughout the myocardial cells of the atrium and to the AV node.
interoceptor:
Sensory receptor that is positioned to interpret stimuli from internal organs, such as stretch receptors in the wall of blood vessels.
interosseous border of the fibula:
Small ridge running down the medial side of the fibular shaft for attachment of the interosseous membrane between the fibula and tibia.
interosseous membrane:
Wide sheet of fibrous connective tissue that fills the gap between two parallel bones, forming a syndesmosis; found between the radius and ulna of the forearm and between the tibia and fibula of the leg.
interphase:
Entire life cycle of a cell, excluding mitosis.
interstitial fluid (IF):
Fluid in the small spaces between cells not contained within blood vessels.
interstitial fluid colloidal osmotic pressure (IFCOP):
Pressure exerted by the colloids within the interstitial fluid.
interstitial fluid hydrostatic pressure (IFHP):
Force exerted by the fluid in the tissue spaces.
intertrochanteric crest:
Short, prominent ridge running between the greater and lesser trochanters on the posterior side of the proximal femur.
intertrochanteric line:
Small ridge running between the greater and lesser trochanters on the anterior side of the proximal femur.
interventricular foramina:
Openings between the lateral ventricles and the third ventricle, allowing for the passage of CSF.
interventricular septum:
Cardiac septum located between the two ventricles.
intervertebral disc:
Structure located between the bodies of adjacent vertebrae that strongly joins the vertebrae; provides padding, weight-bearing ability, and enables vertebral column movements.
intervertebral foramen:
Opening located between adjacent vertebrae for exit of a spinal nerve.
intestinal gland (also crypt of Lieberkühn):
Gland in the small intestinal mucosa that secretes intestinal juice.
intestinal juice:
Mixture of water and mucus that helps absorb nutrients from chyme.
intestinal phase:
Phase of gastric secretion that begins when chyme enters the intestine.
intra-alveolar pressure (intrapulmonary pressure):
Pressure of the air within the alveoli.
intracapsular ligament:
Ligament that is located within the articular capsule of a synovial joint.
intracellular fluid (ICF):
Fluid in the cytosol of cells.
intramembranous ossification:
Process by which bone forms directly from mesenchymal tissue.
intramural ganglia:
Terminal ganglia of the parasympathetic system that are found within the walls of the target effector.
intrapleural pressure:
Pressure of the air within the pleural cavity.
intrinsic factor:
Glycoprotein required for vitamin B12 absorption in the small intestine.
intrinsic ligament:
Ligament that is fused to or incorporated into the wall of the articular capsule of a synovial joint.
intrinsic pathway:
Initial coagulation pathway that begins with vascular damage or contact with foreign substances and results in the activation of the common pathway.
inversion:
Foot movement involving the intertarsal joints of the foot in which the bottom of the foot is turned toward the midline.
involution:
Postpartum shrinkage of the uterus back to its prepregnancy volume.
ion:
Atom with an overall positive or negative charge.
ionic bond:
Attraction between an anion and a cation.
ionotropic receptor:
Neurotransmitter receptor that acts as an ion channel gate and opens by the binding of the neurotransmitter.
ipsilateral:
Word meaning on the same side, as in axons that do not cross the midline in a fibre tract.
iris:
Coloured portion of the anterior eye that surrounds the pupil.
irregular bone:
Bone of complex shape; protects internal organs from compressive forces.
ischemia:
Insufficient blood flow to the tissues.
ischial ramus:
Bony extension projecting anteriorly and superiorly from the ischial tuberosity; joins with the inferior pubic ramus to form the ischiopubic ramus.
ischial spine:
Pointed, bony projection from the posterior margin of the ischium that separates the greater sciatic notch and lesser sciatic notch.
ischial tuberosity:
Large, roughened protuberance that forms the posteroinferior portion of the hip bone; weight-bearing region of the pelvis when sitting.
ischiopubic ramus:
Narrow extension of bone that connects the ischial tuberosity to the pubic body; formed by the junction of the ischial ramus and inferior pubic ramus.
ischium:
Posteroinferior portion of the hip bone.
isometric contraction:
Muscle contraction that occurs with no change in muscle length.
isotonic:
Describes a solution concentration that is the same as a reference concentration.
isotonic contraction:
Muscle contraction that involves changes in muscle length.
isovolumic contraction (also isovolumetric contraction):
Initial phase of ventricular contraction in which tension and pressure in the ventricle increase but no blood is pumped or ejected from the heart.
isovolumic ventricular relaxation phase:
Initial phase of the ventricular diastole when pressure in the ventricles drops below pressure in the two major arteries, the pulmonary trunk and the aorta, and blood attempts to flow back into the ventricles, producing the dicrotic notch of the ECG and closing the two semilunar valves.
isthmus:
Narrow, medial portion of the uterine tube that joins the uterus.
jaundice:
Yellowing of the skin or whites of the eyes due to excess bilirubin in the blood.
jejunum:
Middle part of the small intestine between the duodenum and the ileum.
joint:
Site at which two or more bones or bone and cartilage come together (articulate).
joint cavity:
Space enclosed by the articular capsule of a synovial joint that is filled with synovial fluid and contains the articulating surfaces of the adjacent bones.
jugular (suprasternal) notch:
Shallow notch located on the superior surface of the sternal manubrium.
jugular foramina:
Openings located between the temporal bone and occipital bone that allow the internal jugular vein and three cranial nerves to pass through.
jugular veins:
Blood vessels that return “used” blood from the head and neck.
juxtaglomerular apparatus (JGA):
Located at the juncture of the DCT and the afferent and efferent arterioles of the glomerulus; plays a role in the regulation of renal blood flow and GFR.
juxtaglomerular cell:
Modified smooth muscle cells of the afferent arteriole; secretes renin in response to a drop in blood pressure.
juxtamedullary nephrons:
Nephrons adjacent to the border of the cortex and medulla with loops of Henle that extend into the renal medulla.
keratin:
Type of structural protein that gives skin, hair, and nails its hard, water-resistant properties.
keratinocyte:
Cell that produces keratin and is the most predominant type of cell found in the epidermis.
keratohyalin:
Granulated protein found in the stratum granulosum.
ketone bodies:
Alternative source of energy when glucose is limited, created when too much acetyl CoA is created during fatty acid oxidation.
kinesthesia:
Sense of body movement based on sensations in skeletal muscles, tendons, joints, and the skin.
kinetic energy:
Energy that matter possesses because of its motion.
kinetochore:
Region of a centromere where microtubules attach to a pair of sister chromatids.
knee joint:
Joint that separates the thigh and leg portions of the lower limb; formed by the articulations between the medial and lateral condyles of the femur, and the medial and lateral condyles of the tibia.
Korotkoff sounds:
Noises created by turbulent blood flow through the vessels.
Krebs cycle:
Also called the citric acid cycle or the tricarboxylic acid cycle, converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules.
labial frenulum:
Midline mucous membrane fold that attaches the inner surface of the lips to the gums.
labia majora:
Hair-covered folds of skin located behind the mons pubis.
labia minora:
Thin, pigmented, hairless flaps of skin located medial and deep to the labia majora.
labium:
Lip.
lacrimal bone:
Paired bones that contribute to the anterior-medial wall of each orbit.
lacrimal glands:
Are lateral to the orbit that produces tears to wash across the surface of the eye.
lactase:
Brush border enzyme that breaks down lactose into glucose and galactose.
lactation:
Process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple.
lacteals:
Lymphatic capillaries in the small intestine critical for the transport of dietary lipids and lipid-soluble vitamins to the blood.
lactic acid:
Product of anaerobic glycolysis.
lactiferous ducts:
Ducts that connect the mammary glands to the nipple and allow for the transport of milk.
lactiferous sinus:
Area of milk collection between alveoli and lactiferous duct.
lacunae (singular = lacuna):
Small spaces in bone or cartilage tissue that cells occupy.
lambdoid suture:
Inverted V-shaped joint that unites the occipital bone to the right and left parietal bones on the posterior skull.
lamellae:
Concentric rings of calcified matrix in the centre of each osteon.
lamellated (Pacinian) corpuscles:
Responsible for the detection of deep pressure and vibration.
lamina:
Portion of the vertebral arch on each vertebra that extends between the transverse and spinous process.
lamina propria:
Areolar connective tissue underlying a mucous membrane.
Langerhans cell:
Specialized dendritic cell found in the stratum spinosum that functions as a macrophage.
lanugo:
Silk-like hairs that coat the fetus; shed later in fetal development.
large intestine:
Terminal portion of the alimentary canal.
large motor unit:
Arrangement where a single motor neuron supplies a large number of muscle fibres in a muscle; concerned with simple, or “gross,” movements.
laryngeal prominence:
Region where the two lamine of the thyroid cartilage join, forming a protrusion known as the “Adam’s apple.”
laryngopharynx:
Portion of the pharynx bordered by the oropharynx superiorly and esophagus and trachea inferiorly; serves as a route for both air and food.
larynx:
Cartilaginous structure that produces the voice, prevents food and beverages from entering the trachea, and regulates the volume of air that enters and leaves the lungs.
latch-bridges:
Subset of a cross-bridge in which actin and myosin remain locked together.
latent period:
The time when a twitch does not produce contraction.
lateral:
Describes the side or direction toward the side of the body.
lateral (external) rotation:
Movement of the arm at the shoulder joint or the thigh at the hip joint that moves the anterior surface of the limb away from the midline of the body.
lateral apertures:
Pair of openings from the fourth ventricle to the subarachnoid space on either side and between the medulla and cerebellum.
lateral column:
White matter of the spinal cord between the posterior horn on one side and the axons from the anterior horn on the same side; composed of many different groups of axons, of both ascending and descending tracts, carrying motor commands to and from the brain.
lateral condyle of the femur:
Smooth, articulating surface that forms the distal and posterior sides of the lateral expansion of the distal femur.
lateral condyle of the tibia:
Lateral, expanded region of the proximal tibia that includes the smooth surface that articulates with the lateral condyle of the femur as part of the knee joint.
lateral corticospinal tract:
Division of the corticospinal pathway that travels through the lateral column of the spinal cord and controls appendicular musculature through the lateral motor neurons in the ventral (anterior) horn.
lateral cuneiform:
Most lateral of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, medially with the intermediate cuneiform bone, laterally with the cuboid bone, and anteriorly with the third metatarsal bone.
lateral epicondyle of the femur:
Roughened area of the femur located on the lateral side of the lateral condyle.
lateral excursion:
Side-to-side movement of the mandible away from the midline toward either the right or left side.
lateral flexion:
Bending of the neck or body toward the right or left side.
lateral horn:
Region of the spinal cord grey matter in the thoracic, upper lumbar, and sacral regions that is the central component of the sympathetic division of the autonomic nervous system.
lateralis:
To the outside.
lateral malleolus:
Expanded distal end of the fibula.
lateral meniscus:
C-shaped fibrocartilage articular disc located at the knee, between the lateral condyle of the femur and the lateral condyle of the tibia.
lateral sulcus:
Surface landmark of the cerebral cortex that marks the boundary between the temporal lobe and the frontal and parietal lobes.
lateral tibiofemoral joint:
Portion of the knee consisting of the articulation between the lateral condyle of the tibia and the lateral condyle of the femur; allows for flexion/extension at the knee.
lateral ventricles:
Portions of the ventricular system that are in the region of the cerebrum.
latissimus dorsi:
Broad, triangular axial muscle located on the inferior part of the back.
leakage channel:
Ion channel that opens randomly and is not gated to a specific event, also known as a nongated channel.
leaky tight junctions:
Tight junctions in which the sealing strands of proteins between the membranes of adjacent cells are fewer in number and incomplete; allows limited intercellular movement of solvent and solutes.
left atrioventricular valve (also mitral valve or bicuspid valve):
Valve located between the left atrium and ventricle; consists of two flaps of tissue.
left colic flexure (also splenic flexure):
Point where the transverse colon curves below the inferior end of the spleen.
left gastric artery:
Branch of the celiac trunk; supplies blood to the stomach.
leg:
Portion of the lower limb located between the knee and ankle joints.
lens:
Component of the eye that focuses light on the retina.
leptin:
Protein hormone secreted by adipose tissues in response to food consumption that promotes satiety.
lesser curvature:
The concave medial border.
lesser pelvis (also lesser pelvic cavity or true pelvis):
Narrow space located within the pelvis, defined superiorly by the pelvic brim (pelvic inlet) and inferiorly by the pelvic outlet.
lesser sciatic notch:
Shallow indentation along the posterior margin of the ischium, inferior to the ischial spine.
lesser splanchnic nerve:
Nerve that contains fibres of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the inferior mesenteric ganglion.
lesser trochanter:
Small, bony projection on the medial side of the proximal femur, at the base of the femoral neck.
lesser tubercle:
Small, bony prominence located on the anterior side of the proximal humerus.
letdown reflex:
Release of milk from the alveoli triggered by infant suckling.
leukemia:
Cancer involving leukocytes.
leukocyte (also white blood cell):
Colourless, nucleated blood cell, the chief function of which is to protect the body from disease.
leukocytosis:
Excessive leukocyte proliferation.
leukopenia:
Below-normal production of leukocytes.
Leydig cells:
Cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell.
ligament:
Strong band of dense connective tissue spanning between bones.
ligament of the head of the femur:
Ligament that spans the acetabulum of the hip bone and the fovea capitis of the femoral head.
ligand:
Molecule that binds with specificity to a specific receptor molecule.
ligand-gated channels:
Another name for an ionotropic receptor for which a neurotransmitter is the ligand.
light chain:
Small protein chain of an antibody.
limbic cortex:
Collection of structures of the cerebral cortex that are involved in emotion, memory, and behaviour and are part of the larger limbic system.
limbic lobe:
Structures arranged around the edges of the cerebrum that are involved in memory and emotion.
limbic system:
Structures at the edge (limit) of the boundary between the forebrain and hindbrain that are most associated with emotional behaviour and memory formation.
linea alba:
White, fibrous band that runs along the midline of the trunk.
linea aspera:
Longitudinally running bony ridge located in the middle third of the posterior femur.
lingual frenulum:
Mucous membrane fold that attaches the bottom of the tongue to the floor of the mouth.
lingual glands:
In the lamina propria of the tongue, secrete mucus and a watery serous fluid that contains the enzyme.
lingual lipase:
Digestive enzyme from glands in the tongue that acts on triglycerides.
lingual tonsil:
Lymphoid tissue located at the base of the tongue.
lipid:
Class of nonpolar organic compounds built from hydrocarbons and distinguished by the fact that they are not soluble in water.
lipogenesis:
Synthesis of lipids that occurs in the liver or adipose tissues.
lipolysis:
Breakdown of triglycerides into glycerol and fatty acids.
lipoprotein lipase:
Enzyme that breaks down triglycerides in chylomicrons into fatty acids and monoglycerides.
liver:
Largest gland in the body whose main digestive function is the production of bile.
load:
Resistance to the movement of the handle in a lever system.
lobe:
Glandular tissue in the breast that contains groups of milk-secreting cells.
long bone:
Cylinder-shaped bone that is longer than it is wide; functions as a lever.
longitudinal fissure:
Large separation along the midline between the two cerebral hemispheres.
long reflex:
Reflex arc that includes the central nervous system.
longus:
Long.
loop of Henle:
Descending and ascending portions between the proximal and distal convoluted tubules; those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extend into the medulla.
loose connective tissue (also areolar tissue):
Type of connective tissue proper that shows little specialization, with cells dispersed in the matrix.
lower esophageal sphincter:
Smooth muscle sphincter that regulates food movement from the esophagus to the stomach.
lower motor neuron:
Second neuron in the motor command pathway that is directly connected to the skeletal muscle.
lumbar curve:
Posteriorly concave curvature of the lumbar vertebral column region; a secondary curve of the vertebral column.
lumbar plexus:
Nerve plexus associated with the lumbar spinal nerves.
lumbar puncture:
Procedure used to withdraw CSF from the lower lumbar region of the vertebral column that avoids the risk of damaging CNS tissue because the spinal cord ends at the upper lumbar vertebrae.
lumbar vertebrae:
Five vertebrae numbered L1–L5 that are located in the lumbar region (lower back) of the vertebral column.
lumen:
Interior of a tubular structure such as a blood vessel or a portion of the alimentary canal through which blood, chyme, or other substances travel.
lung:
Organ of the respiratory system that performs gas exchange.
lunula:
Basal part of the nail body that consists of a crescent-shaped layer of thick epithelium.
luteal phase:
Postovulatory phase in the ovarian cycle of progesterone secretion.
luteinizing hormone (LH):
Anterior pituitary hormone that triggers ovulation and the production of ovarian hormones and the production of testosterone.
lymph:
Liquid of the lymphatic system that is returned to the blood.
lymphatic capillaries:
Smallest of the lymphatic vessels and the origin of lymph flow.
lymphatic system:
Network of lymphatic vessels, lymph nodes, and ducts that carries lymph from the tissues and back to the bloodstream.
lymphatic trunks:
Large lymphatics that collect lymph from smaller lymphatic vessels and empty into the blood via lymphatic ducts.
lymphatic vessels:
Vessels for transporting the cells of the immune system.
lymph node:
One of the bean-shaped organs associated with the lymphatic vessels.
lymphocytes:
Agranular leukocytes of the lymphoid stem cell line, many of which function in specific immunity.
lymphoid follicles:
The sites of the formation of lymphocytes, with specific B cell–rich and T cell–rich areas.
lymphoid nodules:
Unencapsulated patches of lymphoid tissue found throughout the body.
lymphoid stem cells:
Type of hematopoietic stem cells that gives rise to lymphocytes, including various T cells, B cells, and NK cells, all of which function in immunity.
lymphoma:
Form of cancer in which masses of malignant T and/or B lymphocytes collect in lymph nodes, the spleen, the liver, and other tissues.
lysosome:
Membrane-bound cellular organelle originating from the Golgi apparatus and containing digestive enzymes.
lysozyme:
Component of saliva that makes it antimicrobial.
macrophage:
Amoeboid phagocyte found in several tissues throughout the body.
macula:
Enlargement at the base of a semicircular canal at which transduction of equilibrium stimuli takes place within the ampulla.
macula densa:
Cells found in the part of the DCT forming the JGA; sense Na+ concentration in the forming urine.
main pancreatic duct (also duct of Wirsung):
Duct through which pancreatic juice drains from the pancreas.
major duodenal papilla:
Point at which the hepatopancreatic ampulla opens into the duodenum.
major histocompatibility complex (MHC):
Gene cluster whose proteins present antigens to T cells.
malleus (also hammer):
Ossicle that is directly attached to the tympanic membrane.
maltase:
Brush border enzyme that breaks down maltose and maltotriose into two and three molecules of glucose, respectively.
mammary glands:
Glands inside the breast that secrete milk.
mandible:
Unpaired bone that forms the lower jawbone; the only movable bone of the skull.
mandibular fossa:
Oval depression located on the inferior surface of the skull.
manubrium:
Expanded, superior portion of the sternum.
marginal arteries:
Branches of the right coronary artery that supply blood to the superficial portions of the right ventricle.
masseter:
Main muscle for chewing that elevates the mandible to close the mouth.
mass movement:
Long, slow, peristaltic wave in the large intestine.
mass number:
Sum of the number of protons and neutrons in the nucleus of an atom.
mast cell:
Cell found in the skin and the lining of body cells that contains cytoplasmic granules with vasoactive mediators such as histamine.
mastication:
Chewing.
mastoid process:
Large bony prominence on the inferior, lateral skull, just behind the earlobe.
matrix:
Extracellular material that is produced by the cells embedded in it, containing ground substance and fibres.
matter:
Physical substance; that which occupies space and has mass.
maxilla (also maxillary bone):
Paired bones that form the upper jaw and anterior portion of the hard palate.
maxillary sinus:
Air-filled space located within each maxillary bone; largest of the paranasal sinuses.
maximus:
Largest.
mean arterial pressure (MAP):
Average driving force of blood to the tissues; approximated by taking diastolic pressure and adding one-third of pulse pressure.
meatus:
One of three recesses (superior, middle, and inferior) in the nasal cavity attached to the conchae that increases the surface area of the nasal cavity.
mechanical digestion:
Chewing, mixing, and segmentation that prepares food for chemical digestion.
mechanically gated channel:
Ion channel that opens when a physical event directly affects the structure of the protein.
mechanoreceptor:
Receptor cell that transduces mechanical stimuli into an electrochemical signal.
meconium:
Fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile.
medial:
Describes the middle or direction toward the middle of the body.
medial (internal) rotation:
Movement of the arm at the shoulder joint or the thigh at the hip joint that brings the anterior surface of the limb toward the midline of the body.
medial condyle of the femur:
Smooth, articulating surface that forms the distal and posterior sides of the medial expansion of the distal femur.
medial condyle of the tibia:
Medial, expanded region of the proximal tibia that includes the smooth surface that articulates with the medial condyle of the femur as part of the knee joint.
medial cuneiform:
Most medial of the three cuneiform tarsal bones; articulates posteriorly with the navicular bone, laterally with the intermediate cuneiform bone, and anteriorly with the first and second metatarsal bones.
medial epicondyle of the femur:
Roughened area of the distal femur located on the medial side of the medial condyle.
medial excursion:
Side-to-side movement that returns the mandible to the midline.
medialis:
To the inside.
medial malleolus:
Bony expansion located on the medial side of the distal tibia.
medial meniscus:
C-shaped fibrocartilage articular disc located at the knee, between the medial condyle of the femur and medial condyle of the tibia.
medial tibiofemoral joint:
Portion of the knee consisting of the articulation between the medial condyle of the tibia and the medial condyle of the femur; allows for flexion/extension at the knee.
median aperture:
Singular opening from the fourth ventricle into the subarachnoid space at the midline between the medulla and cerebellum.
median nerve:
Systemic nerve of the arm, located between the ulnar and radial nerves.
mediastinal artery:
Branch of the thoracic aorta; supplies blood to the mediastinum.
medius:
Medium.
medulla (hair):
In hair, the innermost layer of keratinocytes originating from the hair matrix.
medulla (kidney):
Inner region of the kidney containing the renal pyramids.
medulla (medulla oblongata):
White matter region in the brain that is continuous with the white matter of the spinal cord.
medullary cavity:
Hollow region of the diaphysis; filled with yellow marrow.
megakaryocyte:
Bone marrow cell that produces platelets.
Meissner corpuscle (also tactile corpuscle):
Receptor in the skin that responds to light touch.
melanin:
Pigment that determines the colour of hair and skin.
melanocyte:
Cell found in the stratum basale of the epidermis that produces the pigment melanin.
melanosome:
Intercellular vesicle that transfers melanin from melanocytes into keratinocytes of the epidermis.
melatonin:
Amino acid–derived hormone that is secreted in response to low light and causes drowsiness.
membrane potential:
Distribution of charge across the cell membrane, based on the charges of ions.
memory cell:
Type of B or T lymphocyte that forms after exposure to a pathogen.
memory T cells:
Long-lived immune cell reserved for future exposure to a pathogen.
menarche:
First menstruation in a pubertal female.
meninges:
Protective outer coverings of the CNS composed of connective tissue.
meniscus:
Articular disc.
menses:
Shedding of the inner portion of the endometrium out through the vagina; also referred to as menstruation.
menses phase:
Phase of the menstrual cycle in which the endometrial lining is shed.
menstrual cycle:
Approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase.
Merkel cell:
Receptor cell in the stratum basale of the epidermis that responds to the sense of touch.
merocrine secretion:
Release of a substance from a gland via exocytosis.
mesangial:
Contractile cells found in the glomerulus; can contract or relax to regulate filtration rate.
mesenchymal cell:
Adult stem cell from which most connective tissue cells are derived.
mesoappendix:
Mesentery of the appendix.
mesoderm:
Middle primary embryonic germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys.
mesothelium:
Simple squamous epithelial tissue that covers the major body cavities and is the epithelial portion of serous membranes.
messenger RNA (mRNA):
Nucleotide molecule that serves as an intermediate in the genetic code between DNA and protein.
metabolic acidosis:
Condition wherein a deficiency of bicarbonate causes the blood to be overly acidic.
metabolic alkalosis:
Condition wherein an excess of bicarbonate causes the blood to be overly alkaline.
metabolic rate:
Amount of energy consumed minus the amount of energy expended by the body.
metabolism:
Sum of all catabolic and anabolic reactions that take place in the body.
metabotropic receptor:
Neurotransmitter receptor that involves a complex of proteins that cause metabolic changes in a cell.
metacarpal bone:
One of the five long bones that form the palm of the hand; numbered 1–5, starting on the lateral (thumb) side of the hand.
metaphase:
Second stage of mitosis (and meiosis), characterized by the linear alignment of sister chromatids in the centre of the cell.
metaphase plate:
Linear alignment of sister chromatids in the centre of the cell, which takes place during metaphase.
metarteriole:
Short vessel arising from a terminal arteriole that branches to supply a capillary bed.
metatarsal bone:
One of the five elongated bones that form the anterior half of the foot; numbered 1–5, starting on the medial side of the foot.
micelle:
Tiny lipid-transport compound composed of bile salts and phospholipids with a fatty acid and monoacylglyceride core.
microcirculation:
Blood flow through the capillaries.
microfilament:
The thinnest of the cytoskeletal filaments; composed of actin subunits that function in muscle contraction and cellular structural support.
microglia:
Glial cells that protect the nervous system against infection but are not nervous tissue because they are related to macrophages.
microscopic anatomy:
Study of very small structures of the body using magnification.
microtubule:
The thickest of the cytoskeletal filaments, composed of tubulin subunits that function in cellular movement and structural support.
microvillus:
Small projection of the plasma membrane of the absorptive cells of the small intestinal mucosa.
micturition:
Also called urination or voiding.
midbrain:
Middle region of the adult brain that develops from the mesencephalon.
middle cardiac vein:
Vessel that parallels and drains the areas supplied by the posterior interventricular artery; drains into the great cardiac vein.
middle ear:
Space within the temporal bone between the ear canal and bony labyrinth where the ossicles amplify sound waves from the tympanic membrane to the oval window.
middle nasal concha:
Nasal concha formed by the ethmoid bone that is located between the superior and inferior conchae.
midsagittal or median plane:
Vertical plane that runs directly down the middle of the body.
migrating motility complex:
Form of peristalsis in the small intestine.
mineralocorticoids:
Hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance.
minerals:
Inorganic compounds required by the body to ensure proper function of the body.
minimus:
Smallest.
mitochondrion:
One of the cellular organelles bound by a double lipid bilayer that functions primarily in the production of cellular energy (ATP).
mitosis:
Division of genetic material, during which the cell nucleus breaks down and two new, fully functional nuclei are formed.
mitotic phase:
Phase of the cell cycle in which a cell undergoes mitosis.
mitotic spindle:
Network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis.
mitral valve (also left atrioventricular valve or bicuspid valve):
Valve located between the left atrium and ventricle; consists of two flaps of tissue.
mixing wave:
Unique type of peristalsis that occurs in the stomach.
modelling:
Process, during bone growth, by which bone is resorbed on one surface of a bone and deposited on another.
molar:
Tooth used for crushing and grinding food.
molecule:
Two or more atoms covalently bonded together.
monocyte:
Agranular leukocyte of the myeloid stem cell line that circulates in the bloodstream; tissue monocytes are macrophages.
monoglyceride molecules:
Lipid consisting of a single fatty acid chain attached to a glycerol backbone.
monosaccharide:
Monomer of carbohydrate; also known as a simple sugar.
mons pubis:
Mound of fatty tissue located at the front of the vulva.
morula:
Tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself.
motilin:
Hormone that initiates migrating motility complexes.
motility:
Movement of food through the GI tract.
motor end-plate:
Sarcolemma of muscle fibre at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine.
motor unit:
A motor neuron and the group of muscle fibres it innervates.
movement:
Actions at the joints of the body and the motion of individual organs and even of individual cells.
mucosa (mucous membrane):
Innermost lining of the alimentary canal.
mucosa-associated lymphoid tissue (MALT):
Lymphoid nodule associated with the mucosa.
mucosal barrier:
Protective barrier that prevents gastric juice from destroying the stomach itself.
mucous gland:
Group of cells that secrete mucous, a thick, slippery substance that keeps tissues moist and acts as a lubricant.
mucous membrane (mucosa):
Tissue membrane that is covered by protective mucous and lines tissue exposed to the outside environment.
mucous neck cell:
Gastric gland cell that secretes a uniquely acidic mucus.
mucus:
Alkaline protective coat secreted by the mucus cells in the epithelium.
multiaxial joint:
Type of diarthrosis; a joint that allows for movements within three planes (three axes).
multimodal integration area:
Region of the cerebral cortex in which information from more than one sensory modality is processed to arrive at higher-level cortical functions such as memory, learning, or cognition.
multipennate:
Pennate muscle that has a tendon branching within it.
multipolar:
Shape of a neuron that has multiple processes—the axon and two or more dendrites.
multipotent:
Describes the condition of being able to differentiate into different types of cells within a given cell lineage or a small number of lineages, such as a red blood cell or white blood cell.
murmur:
Unusual heart sound detected by auscultation; typically related to septal or valve defects.
muscarinic receptor:
Type of acetylcholine receptor protein that is characterized by also binding to muscarine and is a metabotropic receptor.
muscle fatigue:
Occurs when a muscle can no longer contract in response to signals from the nervous system.
muscle fibre:
Skeletal muscle cells; they are long and cylindrical.
muscle spindles:
Stretch receptors in the skeletal muscle tissue.
muscle tension:
Force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions.
muscle tissue:
Type of tissue that is capable of contracting and generating tension in response to stimulation; produces movement.
muscle tone:
Low levels of muscle contraction that occur when a muscle is not producing movement.
muscular artery (also distributing artery):
Artery with abundant smooth muscle in the tunica media that branches to distribute blood to the arteriole network.
muscularis:
Muscle (skeletal or smooth) layer of the alimentary canal wall.
myelin:
Lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals.
myelin sheath:
Lipid-rich layer of insulation that surrounds an axon, formed by oligodendrocytes in the CNS and Schwann cells in the PNS; facilitates the transmission of electrical signals.
myeloid stem cells:
Type of hematopoietic stem cell that gives rise to some formed elements, including erythrocytes, megakaryocytes that produce platelets, and a myeloblast lineage that gives rise to monocytes and three forms of granular leukocytes (neutrophils, eosinophils, and basophils).
myenteric plexus (plexus of Auerbach):
Major nerve supply to alimentary canal wall; controls motility.
myocardial contractile cells:
Bulk of the cardiac muscle cells in the atria and ventricles that conduct impulses and contract to propel blood.
myocardium:
Thickest layer of the heart composed of cardiac muscle cells built on a framework of primarily collagenous fibres and blood vessels that supply it and the nervous fibres that help regulate it.
myocyte:
Muscle cells.
myofibril:
Long, cylindrical organelle that runs parallel within the muscle fibre and contains the sarcomeres.
myofilaments:
Highly organized arrangement of the contractile fibres in the sarcomere.
myogenic mechanism:
Mechanism by which smooth muscle responds to stretch by contracting; an increase in blood pressure causes vasoconstriction and a decrease in blood pressure causes vasodilation so that blood flow downstream remains steady.
myogenic response:
Constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network.
myogram:
Instrument used to measure twitch tension.
myometrium:
Smooth muscle layer of the uterus that allows for uterine contractions during labour and expulsion of menstrual blood.
myosin:
Protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fibre.
nail bed:
Layer of epidermis upon which the nail body forms.
nail body:
Main keratinous plate that forms the nail.
nail cuticle (eponychium):
Fold of epithelium that extends over the nail bed, also called the eponychium.
nail fold:
Fold of epithelium that extends over the sides of the nail body, holding it in place.
nail root:
Part of the nail that is lodged deep in the epidermis from which the nail grows.
naive lymphocyte:
Mature B or T cell that has not yet encountered antigen for the first time.
naris (plural = nares):
Opening of the nostrils.
nasal bone:
Bone of the skull that lies under the root and bridge of the nose and is connected to the frontal and maxillary bones.
nasal cavity:
Nares open into this segment of the respiratory system, which is separated into left and right sections by the nasal septum.
nasal conchae (singular = concha):
Serve to swirl the incoming air, which helps warm and moisturize it before the air moves into the delicate air sacs of the lungs.
nasal septum:
Flat, midline structure that divides the nasal cavity into halves, formed by the perpendicular plate of the ethmoid bone, vomer bone, and septal cartilage.
nasolacrimal canal:
Passage for drainage of tears that extends downward from the medial-anterior orbit to the nasal cavity, terminating behind the inferior nasal conchae.
nasopharynx:
The most superior part of the pharynx, which is involved only in breathing and speech.
natural killer (NK) cells:
Cytotoxic lymphocytes capable of recognizing cells that do not express “self” proteins on their plasma membrane or that contain foreign or abnormal markers; provide generalized, nonspecific immunity.
navicular:
Tarsal bone that articulates posteriorly with the talus bone, laterally with the cuboid bone, and anteriorly with the medial, intermediate, and lateral cuneiform bones.
neck of the femur:
Narrowed region located inferior to the head of the femur.
neck of the radius:
Narrowed region immediately distal to the head of the radius.
neck of the rib:
Narrowed region of a rib, next to the rib head.
negative feedback:
Homeostatic mechanism that tends to stabilize an upset in the body’s physiological condition by preventing an excessive response to a stimulus, typically as the stimulus is removed.
negative inotropic factors:
Factors that negatively impact or lower heart contractility.
nephrons:
Functional units of the kidney that carry out all filtration and modification to produce urine; consist of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of Henle; drain into collecting ducts.
nerve:
Cordlike bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system.
nerve plexus:
Network of nerves without neuronal cell bodies included.
nervi vasorum:
Small nerve fibres found in arteries and veins that trigger contraction of the smooth muscle in their walls.
nervous tissue:
Type of tissue that is capable of sending and receiving impulses through electrochemical signals.
net filtration pressure (NFP):
Force driving fluid out of the capillary and into the tissue spaces; equal to the difference of the capillary hydrostatic pressure and the blood colloidal osmotic pressure.
neural fold:
Elevated edge of the neural groove.
neural plate:
Thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue.
neural tube:
Precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium.
neural tunic:
Layer of the eye that contains nervous tissue, namely, the retina.
neurogenic shock:
Type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centres in the medulla oblongata or the nervous fibres originating from this region.
neuroglia (glial cells):
Supportive neural cells.
neuromuscular junction (NMJ):
Synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fibre with receptors for the acetylcholine released by the terminal.
neuron:
Neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system.
neuropeptide:
Neurotransmitter type that includes protein molecules and shorter chains of amino acids.
neurotransmitter:
Signalling chemical released by nerve terminals that binds to and activates receptors on target cells.
neurulation:
Embryonic process that establishes the central nervous system.
neutron:
Heavy subatomic particle having no electrical charge and found in the atom’s nucleus.
neutrophils:
Granulocytes that stain with a neutral dye and are the most numerous of the leukocytes; especially active against bacteria.
nicotinic receptor:
Type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor.
nipple:
External features of the breast surrounded by a pigmented areola.
nociceptor:
Receptor cell that senses pain stimuli.
node of Ranvier:
Gap between two myelinated regions of an axon, allowing for the strengthening of the electrical signal as it propagates down the axon.
nonshivering thermogenesis:
Process of breaking down brown adipose tissue to produce heat in the absence of a shivering response.
norepinephrine:
Secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called noradrenaline.
normal range:
Range of values around the set point that do not cause a reaction by the control centre.
notochord:
Rod-shaped, mesoderm-derived structure that provides support for the growing fetus.
nuclear envelope:
Membrane that surrounds the nucleus, consisting of a double lipid bilayer.
nuclear pore:
One of the small, protein-lined openings found scattered throughout the nuclear envelope.
nucleolus:
Small region of the nucleus that functions in ribosome synthesis.
nucleotide:
Class of organic compounds composed of one or more phosphate groups, a pentose sugar, and a nitrogen-containing base.
nucleus (cell):
Cell’s central organelle; contains the cell’s DNA.
nucleus (nervous system):
In the nervous system, a localized collection of neuron cell bodies that are functionally related; a “centre” of neural function.
nucleus pulposus:
Gel-like central region of an intervertebral disc; provides for padding, weight-bearing, and movement between adjacent vertebrae.
nutrient foramen:
Small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment.
oblique:
At an angle.
obstructive shock:
Type of shock that occurs when a significant portion of the vascular system is blocked.
obturator foramen:
Large opening located in the anterior hip bone, between the pubis and ischium regions.
occipital bone:
Unpaired bone that forms the posterior portions of the brain case and base of the skull.
occipital condyle:
Paired, oval-shaped bony knobs located on the inferior skull, to either side of the foramen magnum.
occipitalis:
Posterior part of the occipitofrontalis muscle.
occipital lobe:
Region of the cerebral cortex directly beneath the occipital bone of the cranium.
occipital sinus:
Enlarged vein that drains the occipital region near the falx cerebelli and flows into the left and right transverse sinuses and also into the vertebral veins.
occipitofrontalis:
Muscle that makes up the scalp with a frontal belly and an occipital belly.
oculomotor nerve:
Third cranial nerve; responsible for contraction of four of the extraocular muscles, the muscle in the upper eyelid, and pupillary constriction.
odorant molecules:
Volatile chemicals that bind to receptor proteins in olfactory neurons to stimulate the sense of smell.
olecranon process:
Expanded posterior and superior portions of the proximal ulna; forms the bony tip of the elbow.
olfaction:
Special sense responsible for smell, which has a unique, direct connection to the cerebrum.
olfactory bulb:
Central target of the first cranial nerve; located on the ventral surface of the frontal lobe in the cerebrum.
olfactory cortex:
That is located in the inferior and medial areas of the temporal lobe.
olfactory epithelium:
Region of the nasal epithelium where olfactory neurons are located.
olfactory hairs:
Dendrites of the olfactory sensory neuron located in the apical surface of the epithelium into the mucus lining the cavity with role in detection of odorant molecules dissolved in the mucus.
olfactory nerve:
First cranial nerve; responsible for the sense of smell.
olfactory sensory neuron:
Receptor cell of the olfactory system, sensitive to the chemical stimuli of smell, the axons of which compose the first cranial nerve.
olfactory tract:
Narrow band of nerve fibres in the brain that connects the olfactory bulb to the primary olfactory cortex.
oligodendrocyte:
Glial cell type in the CNS that provides the myelin insulation for axons in tracts.
oliguria:
Below-normal urine production of 400–500 mL/day.
oocyte:
Cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilization to become a haploid ovum.
oogenesis:
Process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilization, the ovum.
oogonia:
Ovarian stem cells that undergo mitosis during female fetal development to form primary oocytes.
open reduction:
Surgical exposure of a bone to reset a fracture.
opposition:
Thumb movement that brings the tip of the thumb in contact with the tip of a finger.
opsin:
Protein that contains the photosensitive cofactor retinal for phototransduction.
opsonization:
Enhancement of phagocytosis by the binding of antibody or antimicrobial protein.
optic canal:
Opening spanning between middle cranial fossa and posterior orbit.
optic chiasm:
Decussation point in the visual system at which medial retina fibres cross to the other side of the brain.
optic disc:
Spot on the retina at which RGC axons leave the eye and blood vessels of the inner retina pass.
optic nerve:
Second cranial nerve, which is responsible for visual sensation.
oral cavity (also buccal cavity):
Mouth.
oral vestibule:
Part of the mouth bounded externally by the cheeks and lips and internally by the gums and teeth.
orbicularis oculi:
Circular muscle that closes the eye.
orbicularis oris:
Circular muscle that moves the lips.
orbit:
Bony socket that contains the eyeball and associated muscles.
organ:
Functionally distinct structure composed of two or more types of tissues.
organelle:
Any of several different types of membrane-enclosed specialized structures in the cell that perform specific functions for the cell.
organic compound:
Substance that contains both carbon and hydrogen.
organism:
Living being that has a cellular structure and that can independently perform all physiologic functions necessary for life.
organ of Corti:
Structure in the cochlea in which hair cells transduce movements from sound waves into electrochemical signals.
organogenesis:
Development of the rudimentary structures of all of an embryo’s organs from the germ layers.
organ system:
Group of organs that work together to carry out a particular function.
origin:
End of a skeletal muscle that is attached to another structure (usually a bone) in a fixed position.
oropharynx:
Portion of the pharynx flanked by the nasopharynx, oral cavity, and laryngopharynx that is a passageway for both air and food.
orthostatic reflex:
Sympathetic function that maintains blood pressure when standing to offset the increased effect of gravity.
osmoreceptor:
Receptor cell that senses differences in the concentrations of body fluids on the basis of osmotic pressure.
osmosis:
Diffusion of water molecules down their concentration gradient across a selectively permeable membrane.
ossicles:
Three small bones in the middle ear.
ossification (also osteogenesis):
Bone formation.
ossification centre:
Cluster of osteoblasts found in the early stages of intramembranous ossification.
osteoblast:
Cell responsible for forming new bone.
osteoclast:
Cell responsible for resorbing bone.
osteocyte:
Bone cell located within lacunae typically arranged in concentric circles around a central canal.
osteogenic cell:
Undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts.
osteoid:
Uncalcified bone matrix secreted by osteoblasts.
osteon (also Haversian system):
Basic structural unit of compact bone; made of concentric layers of calcified matrix.
otolith:
Layer of calcium carbonate crystals located on top of the otolithic membrane.
otolithic membrane:
Gelatinous substance in the utricle and saccule of the inner ear that contains calcium carbonate crystals and into which the stereocilia of hair cells are embedded.
outer segment:
In the eye, the section of a photoreceptor that contains opsin molecules that transduce light stimuli.
oval window:
Membrane at the base of the cochlea where the stapes attaches, marking the beginning of the scala vestibuli.
ovarian cycle:
Approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase.
ovaries:
Female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone).
ovulation:
Release of a secondary oocyte and associated granulosa cells from an ovary.
ovum:
Haploid female gamete resulting from completion of meiosis II at fertilization.
oxidation:
Loss of an electron.
oxidation-reduction reaction (also redox reaction):
Pair of reactions in which an electron is passed from one molecule to another, oxidizing one and reducing the other.
oxidative phosphorylation:
Process that converts high-energy NADH and FADH2 into ATP.
oxygen debt:
Amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction.
oxygen-hemoglobin dissociation curve:
Graph that describes the relationship of partial pressure to the binding and disassociation of oxygen to and from heme.
oxyhemoglobin (Hb–O
2): Bound form of hemoglobin and oxygen.
oxytocin (OT):
Hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labour, milk ejection during breastfeeding, and feelings of attachment (produced by males and females).
pacemaker:
Cluster of specialized myocardial cells known as the SA node that initiates the sinus rhythm.
Pacinian corpuscle (also lamellated corpuscle):
Receptor in the skin that responds to vibration.
packed cell volume (PCV; also hematocrit):
Volume percentage of erythrocytes present in a sample of centrifuged blood.
palatine bone:
Paired bones that form the posterior quarter of the hard palate and a small area in floor of the orbit.
palatine process:
Medial projection from the maxilla bone that forms the anterior three-quarters of the hard palate.
palatine tonsil:
One of the paired structures composed of lymphoid tissue located anterior to the uvula at the roof of the isthmus of the fauces.
palatoglossal arch:
Muscular fold that extends from the lateral side of the soft palate to the base of the tongue.
palatopharyngeal arch:
Muscular fold that extends from the lateral side of the soft palate to the side of the pharynx.
palmaris longus:
Muscle that provides weak flexion of the hand at the wrist.
palmar venous arches:
Drain the hand and digits and feed into the radial and ulnar veins.
pancreas:
Organ with both exocrine and endocrine functions located posterior to the stomach that is important for digestion and the regulation of blood glucose.
pancreatic amylase:
Enzyme secreted by the pancreas that completes the chemical digestion of carbohydrates in the small intestine.
pancreatic duct:
Duct that fuses with the common bile duct just before entering the duodenum via a common opening.
pancreatic islets:
Specialized clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans.
pancreatic juice:
Secretion of the pancreas containing digestive enzymes and bicarbonate.
pancreatic lipase:
Enzyme secreted by the pancreas that participates in lipid digestion.
pancreatic nuclease:
Enzyme secreted by the pancreas that participates in nucleic acid digestion.
papilla:
For gustation, a bumplike projection on the surface of the tongue that contains taste buds.
papillae:
Extensions of lamina propria of the top and sides of the tongue mucosa.
papillary layer:
Superficial layer of the dermis, made of loose, areolar connective tissue.
papillary muscle:
Extension of the myocardium in the ventricles to which the chordae tendineae attach.
paracrine:
Chemical signal that elicits a response in neighbouring cells; also called paracrine factor.
parallel:
Fascicles that extend in the same direction as the long axis of the muscle.
paranasal sinus:
One of the cavities within the skull that is connected to the conchae that serves to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consists of frontal, maxillary, sphenoidal, and ethmoidal sinuses.
paranasal sinuses:
Cavities within the skull that are connected to the conchae that serve to warm and humidify incoming air, produce mucus, and lighten the weight of the skull; consist of frontal, maxillary, sphenoidal, and ethmoidal sinuses.
parasagittal plane (longitudinal section):
Divides the body into unequal right and left sides.
parasympathetic division:
Division of the autonomic nervous system responsible for restful and digestive functions.
parasympathetic nervous system:
Branch of the autonomic nervous system that conserves energy and calms the body after stress.
parathyroid glands:
Small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone.
parathyroid hormone (PTH):
Peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels.
paravertebral ganglia:
Autonomic ganglia superior to the sympathetic chain ganglia.
parenchyma:
Functional cells of a gland or organ, in contrast with the supportive or connective tissue of a gland or organ.
parietal bone:
Paired bones that form the upper, lateral sides of the skull.
parietal branches (also somatic branches):
Group of arterial branches of the thoracic aorta; include those that supply blood to the thoracic cavity, the vertebral column, and the superior surface of the diaphragm.
parietal cell:
Gastric gland cell that secretes hydrochloric acid and intrinsic factor.
parietal layer:
Serous membrane that lines the walls of the body cavity.
parietal lobe:
Region of the cerebral cortex directly beneath the parietal bone of the cranium.
parietal pericardium:
Layer of serous pericardium that is fused to the fibrous pericardium.
parietal peritoneum:
Lines the abdominal wall.
parietal pleura:
Outermost layer of the pleura that connects to the thoracic wall, mediastinum, and diaphragm.
parieto-occipital sulcus:
Groove in the cerebral cortex representing the border between the parietal and occipital cortices.
parotid gland:
One of a pair of major salivary glands located inferior and anterior to the ears.
partial pressure:
Force exerted by each gas in a mixture of gases.
parturition:
Childbirth.
passive immunity:
Transfer of immunity to a pathogen to an individual that lacks immunity to this pathogen, usually by the injection of antibodies.
passive transport:
Form of transport across the cell membrane that does not require input of cellular energy.
patella:
Kneecap; the largest sesamoid bone of the body; articulates with the distal femur.
patellar ligament:
Ligament spanning from the patella to the anterior tibia; serves as the final attachment for the quadriceps femoris muscle.
patellar surface:
Smooth groove located on the anterior side of the distal femur, between the medial and lateral condyles; site of articulation for the patella.
pectinate muscles:
Muscular ridges seen on the anterior surface of the right atrium.
pectoral girdle:
Shoulder girdle; the set of bones, consisting of the scapula and clavicle, which attaches each upper limb to the axial skeleton.
pectoralis major:
Thick, fan-shaped axial muscle that covers much of the superior thorax.
pectoralis minor:
Muscle that moves the scapula and assists in inhalation.
pedicels:
Fingerlike projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane.
pedicle:
Portion of the vertebral arch that extends from the vertebral body to the transverse process.
pelvic brim:
Pelvic inlet; the dividing line between the greater and lesser pelvic regions; formed by the superior margin of the pubic symphysis, the pectineal lines of each pubis, the arcuate lines of each ilium, and the sacral promontory.
pelvic girdle:
Hip girdle; consists of a single hip bone, which attaches a lower limb to the sacrum of the axial skeleton.
pelvic inlet:
Pelvic brim.
pelvic outlet:
Inferior opening of the lesser pelvis; formed by the inferior margin of the pubic symphysis, the right and left ischiopubic rami and sacrotuberous ligaments, and the tip of the coccyx.
pelvis:
Ring of bone consisting of the right and left hip bones, the sacrum, and the coccyx.
penis:
Male organ of copulation.
pennate:
Fascicles that are arranged differently based on their angles to the tendon.
pepsin:
Enzyme that begins to break down proteins in the stomach.
pepsinogen:
Inactive form of pepsin.
peptide bond:
Covalent bond formed by dehydration synthesis between two amino acids.
perforating canal (also Volkmann’s canal):
Channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum.
perforin:
Molecule in NK cell and cytotoxic T cell granules that forms pores in the membrane of a target cell.
perfusion:
Distribution of blood into the capillaries so the tissues can be supplied.
pericardial cavity:
Cavity surrounding the heart filled with a lubricating serous fluid that reduces friction as the heart contracts.
pericardium (also pericardial sac):
Membrane that separates the heart from other mediastinal structures; consists of two distinct, fused sublayers: the fibrous pericardium and the parietal pericardium.
perichondrium:
Membrane that covers cartilage.
perimetrium:
Outer epithelial layer of the uterine wall.
perimysium:
Connective tissue that bundles skeletal muscle fibres into fascicles within a skeletal muscle.
perineurium:
Layer of connective tissue surrounding fascicles within a nerve.
periodic table of the elements:
Arrangement of the elements in a table according to their atomic number; elements having similar properties because of their electron arrangements compose columns in the table, while elements having the same number of valence shells compose rows in the table.
periodontal ligament:
Band of dense connective tissue that anchors the root of a tooth into the bony jaw socket.
periosteum:
Fibrous membrane covering the outer surface of bone and continuous with ligaments.
peripheral chemoreceptor:
One of the specialized receptors located in the aortic arch and carotid arteries that senses changes in pH, carbon dioxide, or oxygen blood levels.
peripheral nervous system (PNS):
Anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely, all parts except the brain and spinal cord.
peripheral protein:
Membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane.
peripheral tolerance:
Mature B cell made tolerant by lack of T cell help.
peristalsis:
Muscular contractions and relaxations that propel food through the GI tract.
peritoneal cavity:
The space bounded by the visceral and parietal peritoneal surfaces.
peritoneal fold:
Large folds that envelop various abdominal organs, holding them to the dorsal surface of the body wall.
peritoneum:
Broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue that holds in place the digestive organs within the abdominal cavity.
peritubular capillaries:
Second capillary bed of the renal portal system; surround the proximal and distal convoluted tubules; associated with the vasa recta.
permanent tooth:
One of 32 adult teeth.
peroxisome:
Membrane-bound organelle that contains enzymes primarily responsible for detoxifying harmful substances.
perpendicular plate of the ethmoid bone:
Downward, midline extension of the ethmoid bone that forms the superior portion of the nasal septum.
Peyer’s patches:
A type of MALT in the small intestine important for immune responses against ingested substances.
pH:
Negative logarithm of the hydrogen-ion (H+) concentration of a solution.
phagocytosis:
Movement of material from the outside to the inside of the cells via vesicles made from invaginations of the plasma membrane.
phalanx bone (plural = phalanges):
One of the 28 bones that form the fingers, thumbs, and toes.
pharyngeal tonsil:
Structure composed of lymphoid tissue located in the nasopharynx.
pharynx:
Region of the conducting zone that forms a tube of skeletal muscle lined with respiratory epithelium; located between the nasal conchae and the esophagus and trachea.
philtrum:
Concave surface of the face that connects the apex of the nose to the top lip.
phospholipid:
A lipid compound in which a phosphate group is combined with a diglyceride.
phosphorylation:
Addition of one or more phosphate groups to an organic compound.
photoreceptor:
Receptor cell specialized to respond to light stimuli.
phrenic nerve:
Systemic nerve from the cervical plexus that innervates the diaphragm.
physiological sphincter:
Sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak.
physiology:
Science that studies the chemistry, biochemistry, and physics of the body’s functions.
pia mater:
Thin, innermost membrane of the meninges that directly covers the surface of the CNS.
pineal gland:
Endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle.
pinealocyte:
Cell of the pineal gland that produces and secretes the hormone melatonin.
pinocytosis:
Endocytosis of fluid.
pituitary dwarfism:
Disorder in children caused when abnormally low levels of GH result in growth retardation.
pituitary gland:
Bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis).
pivot joint:
Synovial joint at which the rounded portion of a bone rotates within a ring formed by a ligament and an articulating bone; functionally classified as uniaxial joint.
placenta:
Organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus.
placenta previa:
Low placement of fetus within the uterus that causes the placenta to partially or completely cover the opening of the cervix as it grows.
placentation:
Formation of the placenta; complete by weeks 14–16 of pregnancy.
plane:
Imaginary two-dimensional surface that passes through the body.
plane joint:
Synovial joint formed between the flattened articulating surfaces of adjacent bones; functionally classified as a multiaxial joint.
plantar flexion:
Foot movement at the ankle in which the heel is lifted off the ground.
plasma:
In blood, the liquid extracellular matrix composed mostly of water that circulates the formed elements and dissolved materials throughout the cardiovascular system.
plasma cell:
One form of B cells that produces the antibodies or immunoglobulins.
plasma osmolality:
Ratio of solutes to a volume of solvent in the plasma; plasma osmolality reflects a person’s state of hydration.
plasmin:
Blood protein active in fibrinolysis.
plateau phase:
Long refractory periods required for the cardiac muscle cells to pump blood effectively before they are capable of firing for a second time.
platelet plug:
Accumulation and adhesion of platelets at the site of blood vessel injury.
platelets (also thrombocytes):
One of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.
pleura:
Serous membrane that lines the pleural cavity and covers the lungs.
pleural cavity:
Cavity in the thoracic cavity that surrounds the lungs.
pleural fluid:
Substance that acts as a lubricant for the visceral and parietal layers of the pleura during the movement of breathing.
plexus:
Network of nerves or nervous tissue.
pluripotent:
Describes the condition of being able to differentiate into a large variety of cell types.
pluripotent stem cell:
Stem cell that derives from totipotent stem cells and is capable of differentiating into many, but not all, cell types.
pneumotaxic centre:
Network of neurons within the pons that inhibits the activity of the neurons in the dorsal respiratory group; controls rate of breathing.
podocytes:
Cells forming fingerlike processes; form the visceral layer of Bowman’s capsule; pedicels of the podocytes interdigitate to form a filtration membrane.
polar body:
Smaller cell produced during the process of meiosis in oogenesis.
polar molecule:
Molecule covalently bonded where one atom is more electronegative and draws electrons toward its nucleus, resulting in slight negative and positive charges.
pollex:
Thumb; digit 1 of the hand.
polyclonal response:
Response by multiple clones to a complex antigen with many determinants.
polymorphonuclear neutrophil:
White blood cells with a lobed nucleus.
polypeptide:
Chain of amino acids linked by peptide bonds.
polyribosome:
Simultaneous translation of a single mRNA transcript by multiple ribosomes.
polysaccharides:
Complex carbohydrates made up of many monosaccharides.
polyspermy:
Penetration of an oocyte by more than one sperm.
polyuria:
Urine production in excess of 2.5 L/day; may be caused by diabetes insipidus, diabetes mellitus, or excessive use of diuretics.
popliteal fossa:
Diamond-shaped space at the back of the knee.
popliteus:
Muscle that flexes the leg at the knee and creates the floor of the popliteal fossa.
porta hepatis:
“gateway to the liver” where the hepatic artery and hepatic portal vein enter the liver.
portal triad:
Bile duct, hepatic artery branch, and hepatic portal vein branch.
positive chemotaxis:
Process in which a cell is attracted to move in the direction of chemical stimuli.
positive feedback:
Mechanism that intensifies a change in the body’s physiological condition in response to a stimulus.
positive inotropic factors:
Factors that positively impact or increase heart contractility.
postabsorptive state:
Also called the fasting state; the metabolic state occurring after digestion, when food is no longer the body’s source of energy and it must rely on stored glycogen.
postcentral gyrus:
Primary motor cortex located in the frontal lobe of the cerebral cortex.
posterior:
Describes the back or direction toward the back of the body; also referred to as dorsal.
posterior arch:
Posterior portion of the ringlike C1 (atlas) vertebra.
posterior cardiac vein:
Vessel that parallels and drains the areas supplied by the marginal artery branch of the circumflex artery; drains into the great cardiac vein.
posterior cavity:
Posterior body cavity that houses the brain and spinal cord; also referred to as dorsal cavity.
posterior columns:
White matter of the spinal cord that lies between the posterior horns of the grey matter, sometimes referred to as the dorsal column; composed of axons of ascending tracts that carry sensory information up to the brain.
posterior cruciate ligament:
Intracapsular ligament of the knee; extends from the posterior, superior surface of the tibia to the inner aspect of the medial condyle of the femur; prevents anterior displacement of the femur when the knee is flexed and weight-bearing.
posterior horn:
Grey matter region of the spinal cord in which sensory input arrives, sometimes referred to as the dorsal horn.
posterior interventricular artery (also posterior descending artery):
Branch of the right coronary artery that runs along the posterior portion of the interventricular sulcus toward the apex of the heart and gives rise to branches that supply the interventricular septum and portions of both ventricles.
posterior interventricular sulcus:
Sulcus located between the left and right ventricles on the posterior surface of the heart.
posterior median sulcus:
Midline feature of the posterior spinal cord, marking the separation between right and left sides of the cord.
posterior pituitary (neurohypophysis):
Extension of the neurons of the paraventricular and supraoptic nuclei of the hypothalamus.
postganglionic fibre:
Axon from a ganglionic neuron in the autonomic nervous system that projects to and synapses with the target effector; sometimes referred to as a postganglionic neuron.
postsynaptic potential (PSP):
Graded potential in the postsynaptic membrane caused by the binding of neurotransmitter to protein receptors.
potential energy:
Stored energy matter possesses because of the positioning or structure of its components.
power stroke:
Action of myosin pulling actin inward (toward the M line).
PP cell:
Minor cell type in the pancreas that secretes the hormone pancreatic polypeptide.
precapillary sphincters:
Circular rings of smooth muscle that surround the entrance to a capillary and regulate blood flow into that capillary.
precentral gyrus:
Ridge just posterior to the central sulcus, in the parietal lobe, where somatosensory processing initially takes place in the cerebrum.
prefrontal lobe:
Specific region of the frontal lobe anterior to the more specific motor function areas, which can be related to the early planning of movements and intentions to the point of being personality-type functions.
preganglionic fibre:
Axon from a central neuron in the autonomic nervous system that projects to and synapses with a ganglionic neuron; sometimes referred to as a preganglionic neuron.
preload (also end diastolic volume):
Amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction.
premolar (also bicuspid):
Transitional tooth used for mastication, crushing, and grinding food.
premotor area:
Region of the frontal lobe responsible for planning movements that will be executed through the primary motor cortex.
premotor cortex:
Cortical area anterior to the primary motor cortex that is responsible for planning movements.
prepotential depolarization (also spontaneous depolarization):
Mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise.
prepuce (also foreskin):
Flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred to as the foreskin.
prevertebral ganglia:
Autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia.
primary adaptive response:
Immune system’s response to the first exposure to a pathogen.
primary bronchi:
Bronchi that enter the lungs at the hilum.
primary curve:
Anteriorly concave curvatures of the thoracic and sacrococcygeal regions that are retained from the original fetal curvature of the vertebral column.
primary follicles:
Ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells.
primary germ layers:
The endoderm, mesoderm, and ectoderm.
primary lymphoid organ:
Site where lymphocytes mature and proliferate; red bone marrow and thymus gland.
primary oocytes:
Formed from ogonia in the fetal ovary prior to birth.
primary ossification centre:
Region, deep in the periosteal collar, where bone development starts during endochondral ossification.
primary sensory cortex:
Region of the cerebral cortex that initially receives sensory input from an ascending pathway from the thalamus and begins the processing that will result in conscious perception of that modality.
primary spermatocyte:
Cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids.
prime mover (also agonist):
Principal muscle involved in an action.
primitive streak:
Indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation.
primordial follicles:
Least-developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells.
principal cells:
Found in collecting ducts and possess channels for the recovery or loss of sodium and potassium; under the control of aldosterone; also have aquaporin channels under ADH control to regulate recovery of water.
process:
In cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites.
product:
One or more substances produced by a chemical reaction.
progesterone:
Predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy.
projection:
Bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach.
prolactin (PRL):
Anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk.
proliferative phase:
Phase of the menstrual cycle in which the endometrium proliferates.
promoter:
Region of DNA that signals transcription to begin at that site within the gene.
pronated position:
Forearm position in which the palm faces backward.
pronation:
Forearm motion that moves the palm of the hand from the palm forward to the palm backward position.
pronator quadratus:
Pronator that originates on the ulna and inserts on the radius.
pronator teres:
Pronator that originates on the humerus and inserts on the radius.
prone:
Face down.
propagation:
Movement of an action potential along the length of an axon.
prophase:
First stage of mitosis (and meiosis), characterized by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes.
proprioception:
General sensory perceptions providing information about the location and movement of body parts; the “sense of the self.”
proprioceptor:
Receptor cell that senses changes in the position and kinesthetic aspects of the body.
propulsion:
Voluntary process of swallowing and the involuntary process of peristalsis that moves food through the digestive tract.
prostaglandin:
Lipid compound derived from fatty acid chains; important in regulating several body processes.
prostate gland, or prostate:
Doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation.
protein:
Class of organic compounds that are composed of many amino acids linked together by peptide bonds.
protein kinase:
Enzyme that initiates a phosphorylation cascade upon activation.
proteolysis:
Process of breaking proteins into smaller peptides.
proton:
Heavy subatomic particle having a positive charge and found in the atom’s nucleus.
protraction:
Anterior motion of the scapula or mandible.
proximal:
Describes a position nearer to the point of attachment or the trunk of the body.
proximal convoluted tubules (PCTs):
Tortuous tubules receiving filtrate from Bowman’s capsule; most active part of the nephron in reabsorption and secretion.
proximal radioulnar joint:
Articulation between head of radius and radial notch of ulna; uniaxial pivot joint that allows for rotation of radius during pronation/supination of the forearm.
pseudostratified columnar epithelium:
Tissue that consists of a single layer of irregularly shaped and sized cells that give the appearance of multiple layers; found in ducts of certain glands and the upper respiratory tract.
psoas major:
Muscle that, along with the iliacus, makes up the iliopsoas.
pubic arch:
Bony structure formed by the pubic symphysis and the bodies and inferior pubic rami of the adjacent pubic bones.
pubic body:
Enlarged, medial portion of the pubis region of the hip bone.
pubic symphysis:
Joint formed by the articulation between the pubic bodies of the right and left hip bones.
pubis:
Anterior portion of the hip bone.
pulmonary artery:
One of two branches, left and right, that divides off from the pulmonary trunk and leads to smaller arterioles and eventually to the pulmonary capillaries.
pulmonary capillaries:
Capillaries surrounding the alveoli of the lungs where gas exchange occurs: Carbon dioxide exits the blood and oxygen enters.
pulmonary circuit:
System of blood vessels that provides gas exchange via a network of arteries, veins, and capillaries that run from the heart, through the body, and back to the lungs.
pulmonary surfactant:
Substance composed of phospholipids and proteins that reduces the surface tension of the alveoli; made by type II alveolar cells.
pulmonary trunk:
Large arterial vessel that carries blood ejected from the right ventricle; divides into the left and right pulmonary arteries.
pulmonary valve (also pulmonary semilunar valve, pulmonic valve, or right semilunar valve):
Valve at the base of the pulmonary trunk that prevents backflow of blood into the right ventricle; consists of three flaps.
pulmonary veins:
Veins that carry highly oxygenated blood into the left atrium, which pumps the blood into the left ventricle, which in turn pumps oxygenated blood into the aorta and to the many branches of the systemic circuit.
pulmonary ventilation:
Exchange of gases between the lungs and the atmosphere; breathing.
pulp cavity:
Deepest portion of a tooth, containing nerve endings and blood vessels.
pulse:
Alternating expansion and recoil of an artery as blood moves through the vessel; an indicator of heart rate.
pulse pressure:
Difference between the systolic and diastolic pressures.
pupil:
Open hole at the centre of the iris that light passes through into the eye.
Purkinje cell:
A multipolar neuron that has a very important role to play in the cerebellum.
Purkinje fibres:
Specialized myocardial conduction fibres that arise from the bundle branches and spread the impulse to the myocardial contraction fibres of the ventricles.
P wave:
Component of the electrocardiogram that represents the depolarization of the atria.
pyloric antrum:
Wider, more superior part of the pylorus.
pyloric canal:
Narrow, more inferior part of the pylorus.
pyloric sphincter:
Sphincter that controls stomach emptying.
pylorus:
Lower, funnel-shaped part of the stomach that is continuous with the duodenum.
pyramidal decussation:
Location at which corticospinal tract fibres cross the midline and segregate into the anterior and lateral divisions of the pathway.
pyramids:
Segment of the descending motor pathway that travels in the anterior position of the medulla.
pyruvate:
Three-carbon end product of glycolysis and starting material that is converted into acetyl CoA that enters the Krebs cycle.
pyruvic acid:
Product of glycolysis that can be used in aerobic respiration or converted to lactic acid.
QRS complex:
Component of the electrocardiogram that represents the depolarization of the ventricles and includes, as a component, the repolarization of the atria.
quadriceps femoris group:
Four muscles that extend and stabilize the knee.
quadriceps tendon (also patellar tendon):
Tendon common to all four quadriceps muscles, inserts into the patella.
quickening:
Fetal movements that are strong enough to be felt by the mother.
quiet breathing (also eupnea):
Mode of breathing that occurs at rest and does not require the cognitive thought of the individual.
radial artery:
Formed at the bifurcation of the brachial artery; parallels the radius; gives off smaller branches until it reaches the carpal region, where it fuses with the ulnar artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region.
radial collateral ligament:
Intrinsic ligament on the lateral side of the elbow joint; runs from the lateral epicondyle of humerus to merge with the annular ligament.
radial nerve:
Systemic nerve of the arm, the distal component of which is located near the radial bone.
radial tuberosity:
Oval-shaped, roughened protuberance located on the medial side of the proximal radius.
radial vein:
Parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein.
radiation:
Transfer of heat via infrared waves.
radiocarpal joint:
Wrist joint; located between the forearm and hand regions of the upper limb; articulation formed proximally by the distal end of the radius and the fibrocartilaginous pad that unites the distal radius and ulna bone, and distally by the scaphoid, lunate, and triquetrum carpal bones.
radius:
Bone located on the lateral side of the forearm.
ramus of the mandible:
Vertical portion of the mandible.
reabsorption:
In the cardiovascular system, the movement of material from the interstitial fluid into the capillaries.
reactant:
One or more substances that enter into the reaction.
receptor:
Protein molecule that contains a binding site for another specific molecule (called a ligand).
receptor-mediated endocytosis:
Endocytosis of ligands attached to membrane-bound receptors.
receptor potential:
Graded potential in a specialized sensory cell that directly causes the release of neurotransmitter without an intervening action potential.
recruitment:
Increase in the number of motor units involved in contraction.
rectal valve:
One of three transverse folds in the rectum where feces are separated from flatus.
rectum:
Part of the large intestine between the sigmoid colon and anal canal.
rectus:
Straight.
rectus abdominis:
Long, linear muscle that extends along the middle of the trunk.
rectus femoris:
Quadricep muscle on the anterior aspect of the thigh.
rectus sheaths:
Tissue that makes up the linea alba.
red blood cells (RBCs; also erythrocytes):
One of the formed elements of blood that transports oxygen.
red marrow:
Connective tissue within the spaces of spongy (cancellous) bone tissue; site of hematopoiesis.
red nucleus:
Midbrain nucleus that sends corrective commands to the spinal cord along the rubrospinal tract, based on the disparity between an original command and the sensory feedback from movement.
red pulp:
Splenic nodule area consisting of mostly red blood cells.
reduction:
Gaining of an electron.
referred pain:
The conscious perception of visceral sensation projected to a different region of the body, such as the left shoulder and arm pain as a sign of a heart attack.
reflex arc:
Circuit of a reflex that involves a sensory input and motor output, or an afferent branch and an efferent branch, and an integrating centre to connect the two branches.
refractory period:
Time after the initiation of an action potential when another action potential cannot be generated.
regional anatomy:
Study of the structures that contribute to specific body regions.
regulatory T cells (Treg; also suppressor T cells):
Class of CD4 T cells that regulates other T cell responses.
relative refractory period:
Time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K+ channels are not closed.
relaxation phase:
Period after twitch contraction when tension decreases.
releasing hormones:
Hormones that stimulate the secretion of hormones from the anterior pituitary.
remodelling:
Process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed.
renal artery:
Branch of the abdominal aorta; supplies each kidney.
renal columns:
Extensions of the renal cortex into the renal medulla; separate the renal pyramids; contain blood vessels and connective tissues.
renal corpuscle:
Consists of the glomerulus and Bowman’s capsule.
renal cortex:
Outer part of the kidney containing all of the nephrons; some nephrons have loops of Henle extending into the medulla.
renal hilum:
Recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass.
renal papillae:
Medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces.
renal pyramids:
Six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons.
renal vein:
Largest vein entering the inferior vena cava; drains the kidneys and leads to the inferior vena cava.
renin:
Enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyzes the conversion of angiotensinogen into angiotensin I.
renin-angiotensin-aldosterone system (RAAS):
Hormone system that has specialized cells of the kidneys secrete the enzyme renin in response to low blood volume or low blood pressure.
repolarization:
Return of the membrane potential to its normally negative voltage at the end of the action potential.
reposition:
Movement of the thumb from opposition back to the anatomical position (next to index finger).
reproduction:
Process by which new organisms are generated.
residual volume (RV):
Amount of air that remains in the lungs after maximum exhalation.
resistance:
Property of an axon that relates to the ability of particles to diffuse through the cytoplasm; this is inversely proportional to the fibre diameter.
respiratory acidosis:
Condition wherein an excess of carbonic acid or CO2 causes the blood to be overly acidic.
respiratory alkalosis:
Condition wherein a deficiency of carbonic acid/CO2 levels causes the blood to be overly alkaline.
respiratory bronchiole:
Specific type of bronchiole that leads to alveolar sacs.
respiratory cycle:
One sequence of inspiration and expiration.
respiratory epithelium:
Ciliated lining of much of the conducting zone that is specialized to remove debris and pathogens and produce mucus.
respiratory membrane:
Alveolar and capillary wall together, which form an air-blood barrier that facilitates the simple diffusion of gases.
respiratory pump:
Increase in the volume of the thorax during inhalation that decreases air pressure, enabling venous blood to flow into the thoracic region; then exhalation increases pressure, moving blood into the atria.
respiratory rate:
Total number of breaths taken each minute.
respiratory volume:
Varying amounts of air within the lung at a given time.
respiratory zone:
Includes structures of the respiratory system that are directly involved in gas exchange.
response:
Nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli.
responsiveness:
Ability of an organism or a system to adjust to changes in conditions.
rest and digest:
Set of functions associated with the parasympathetic system that lead to restful actions and digestion.
resting membrane potential:
The difference in voltage measured across a cell membrane under steady-state conditions, typically −70 mV.
reticular fibre:
Fine fibrous protein, made of collagen subunits, which cross-link to form supporting “nets” within connective tissue.
reticular formation:
Diffuse region of grey matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness.
reticular lamina:
Matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane.
reticular layer:
Deeper layer of the dermis; it has a reticulated appearance due to the presence of abundant collagen and elastin fibres.
reticular tissue:
Type of loose connective tissue that provides a supportive framework to soft organs, such as the lymphatic tissue, spleen, and liver.
reticulocyte:
Immature erythrocyte that may still contain fragments of organelles.
reticuloendothelial cell (also Kupffer cell):
Phagocyte in hepatic sinusoids that filters out material from venous blood from the alimentary canal.
reticulospinal tract:
Extrapyramidal connections between the brain stem and spinal cord that modulate movement, contribute to posture, and regulate muscle tone.
retina:
Nervous tissue of the eye at which phototransduction takes place.
retinal ganglion cell (RGC):
Neuron of the retina that projects along the second cranial nerve.
retraction:
Posterior motion of the scapula or mandible.
retroperitoneal:
Behind the peritoneum; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall.
Rh blood group:
Blood-type classification based on the presence or absence of the antigen Rh on the erythrocyte membrane surface.
rhodopsin:
Photopigment molecule found in the rod photoreceptors.
rhomboid major:
Muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae.
rhomboid minor:
Muscle that attaches the vertebral border of the scapula to the spinous process of the thoracic vertebrae.
ribonuclease:
Pancreatic enzyme that digests RNA.
ribonucleic acid (RNA):
Ribose-containing nucleotide that helps manifest the genetic code as protein.
ribosomal RNA (rRNA):
RNA that makes up the subunits of a ribosome.
ribosome:
Cellular organelle that functions in protein synthesis.
ribs:
Thin, curved bones of the chest wall.
right atrioventricular valve (also tricuspid valve):
Valve located between the right atrium and ventricle; consists of three flaps of tissue.
right colic flexure (also hepatic flexure):
Point at the inferior surface of the liver where the ascending colon turns abruptly to the left.
right lymphatic duct:
Drains lymph fluid from the upper right side of the body into the right subclavian vein.
RNA polymerase:
Enzyme that unwinds DNA and then adds new nucleotides to a growing strand of RNA for the transcription phase of protein synthesis.
rod photoreceptor:
One of the two types of retinal receptor cell that is specialized for low-light vision.
root (nose):
Region of the external nose between the eyebrows.
root (tooth):
Portion of a tooth embedded in the alveolar processes beneath the gum line.
rotation:
Movement of a bone around a central axis (atlantoaxial joint) or around its long axis (proximal radioulnar joint; shoulder or hip joint); twisting of the vertebral column resulting from the summation of small motions between adjacent vertebrae.
rotator cuff:
Strong connective tissue structure formed by the fusion of four rotator cuff muscle tendons to the articular capsule of the shoulder joint; surrounds and supports superior, anterior, lateral, and posterior sides of the humeral head.
rough ER (RER):
Organelle that function as the site for protein synthesis; many ribosomes attach to the ER giving it the studded appearance of rough ER.
round window:
Membrane that marks the end of the scala tympani.
rubrospinal tract:
Descending motor control pathway, originating in the red nucleus, that mediates control of the limbs on the basis of cerebellar processing.
rugae:
Folds of alimentary canal mucosa and submucosa in the empty stomach and other organs.
rugae (of the vagina):
Folds of skin in the vagina that allow it to stretch during intercourse and childbirth.
saccule:
Structure of the inner ear responsible for transducing linear acceleration in the vertical plane.
sacral canal:
Bony tunnel that runs through the sacrum.
sacral foramina:
Series of paired openings for nerve exit located on both the anterior (ventral) and posterior (dorsal) aspects of the sacrum.
sacral hiatus:
Inferior opening and termination of the sacral canal.
sacral plexus:
Nerve plexus associated with the lower lumbar and sacral spinal nerves.
sacral promontory:
Anterior lip of the base (superior end) of the sacrum.
sacrococcygeal curve:
Anteriorly concave curvature formed by the sacrum and coccyx; a primary curve of the vertebral column.
sacroiliac joint:
Joint formed by the articulation between the auricular surfaces of the sacrum and ilium.
sacrum:
Single bone located near the inferior end of the adult vertebral column that is formed by the fusion of five sacral vertebrae; forms the posterior portion of the pelvis.
saddle joint:
Synovial joint in which the articulating ends of both bones are convex and concave in shape, such as the first carpometacarpal joint at the base of the thumb; functionally classified as a biaxial joint.
sagittal plane:
Two-dimensional, vertical plane that divides the body or organ into right and left sides.
sagittal suture:
Joint that unites the right and left parietal bones at the midline along the top of the skull.
saliva:
Aqueous solution of proteins and ions secreted into the mouth by the salivary glands.
salivary amylase:
Digestive enzyme that is found in the saliva and begins the digestion of carbohydrates in the mouth.
salivary gland:
Exocrine gland that secretes a digestive fluid called saliva.
salivation:
Secretion of saliva.
saltatory conduction:
Quick propagation of the action potential along a myelinated axon owing to voltage-gated Na+ channels being present only at the nodes of Ranvier.
saphenous nerve:
Systemic nerve of the lower anterior leg that is a branch from the femoral nerve.
sarcolemma:
Plasma membrane of a skeletal muscle fibre.
sarcomere:
Longitudinally repeating functional unit of skeletal muscle, with all the contractile and associated proteins involved in contraction.
sarcoplasm:
Cytoplasm of a muscle cell.
sarcoplasmic reticulum (SR):
Specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca++.
sartorius:
Bandlike muscle that flexes, abducts, and laterally rotates the leg at the hip.
satellite cell:
Glial cell type in the PNS that provides support for neurons in the ganglia.
scala tympani:
Portion of the cochlea that extends from the apex to the round window.
scala vestibuli:
Portion of the cochlea that extends from the oval window to the apex.
scalene muscles:
Flex, laterally flex, and rotate the head; contribute to deep inhalation.
scapula:
Shoulder blade bone located on the posterior side of the shoulder.
Schwann cell:
Glial cell type in the PNS that provides the myelin insulation for axons in nerves.
sciatic nerve:
Systemic nerve from the sacral plexus that is a combination of the tibial and fibular nerves and extends across the hip joint and gluteal region into the upper posterior leg.
sclera:
White of the eye.
scrotum:
External pouch of skin and muscle that houses the testes.
sebaceous gland:
Type of oil gland found in the dermis all over the body and helps lubricate and waterproof the skin and hair by secreting sebum.
sebum:
Oily substance that is composed of a mixture of lipids that lubricates the skin and hair.
secondary active transport:
Process harnessing an electrochemical gradient established by primary active transport to drive the transport of a second molecule.
secondary adaptive response:
Immune response observed upon reexposure to a pathogen, which is stronger and faster than a primary response.
secondary curve:
Posteriorly concave curvatures of the cervical and lumbar regions of the vertebral column that develop after the time of birth.
secondary follicles:
Ovarian follicles with a primary oocyte and multiple layers of granulosa cells.
secondary lymphoid organs:
Sites where lymphocytes mount adaptive immune responses; examples include lymph nodes and spleen.
secondary oocyte:
Daughter oocyte resulting from meiosis in a primary oocyte; leaves the ovary during ovulation.
secondary ossification centre:
Region of bone development in the epiphyses.
secondary spermatocytes:
Products of meiosis I in primary spermatocytes, where each of the 23 pairs of chromosomes separates resulting in two cells, each with only half the number of chromosomes.
second messenger:
Molecule that initiates a signalling cascade in response to hormone binding on a cell membrane receptor and activation of a G protein.
secretin:
Hormone released in the small intestine to aid in digestion.
secretory phase:
Phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo.
section:
A single flat surface of a three-dimensional structure that has been cut through.
segmentation:
Alternating contractions and relaxations of nonadjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive juices.
selective permeability:
Feature of any barrier that allows certain substances to cross but excludes others.
sella turcica:
Elevated area of sphenoid bone located at the midline of the middle cranial fossa.
semen:
Ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands.
semicircular canals:
Structures within the inner ear responsible for transducing rotational movement information.
semilunar valves:
Valves located at the base of the pulmonary trunk and at the base of the aorta.
semimembranosus:
Hamstring muscle.
seminal vesicle:
Gland that produces seminal fluid, which contributes to semen.
seminiferous tubules:
Tube structures within the testes where spermatogenesis occurs.
semitendinosus:
Hamstring muscle.
sensation:
Nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue.
sensor (also receptor):
Reports a monitored physiological value to the control centre.
sensory ganglia:
Clusters of nerve cell bodies located outside the central nervous system that relay sensory information.
sensory homunculus:
Topographic representation of the body within the somatosensory cortex demonstrating the correspondence between neurons processing stimuli and sensitivity.
sensory modality:
A particular system for interpreting and perceiving environmental stimuli by the nervous system.
sensory receptor:
Nervous structures specialized for detection of temperature, touch, pain, and so on.
sepsis (also septicemia):
Organismal-level inflammatory response to a massive infection.
septal cartilage:
Flat cartilage structure that forms the anterior portion of the nasal septum.
septic shock (also blood poisoning):
Type of shock that follows a massive infection resulting in organism-wide inflammation.
septum (plural = septa):
Walls or partitions that divide the heart into chambers.
serosa:
Outermost layer of the alimentary canal wall present in regions within the abdominal cavity.
serous gland:
Group of cells within the serous membrane that secrete a lubricating substance onto the surface.
serous membrane (serosa):
Type of tissue membrane that lines body cavities and lubricates them with serous fluid.
serous pericardium:
Delicate layer that also consists of two layers: the parietal pericardium and the visceral pericardium (epicardium).
serratus anterior:
Large and flat muscle that originates on the ribs and inserts onto the scapula.
Sertoli cells:
Cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell.
serum:
Blood plasma that does not contain clotting factors.
sesamoid bone:
Small, round bone embedded in a tendon; protects the tendon from compressive forces.
set point:
Ideal value for a physiological parameter; the level or small range within which a physiological parameter, such as blood pressure, is stable and optimally healthful—that is, within its parameters of homeostasis.
shaft of the clavicle:
Body of the clavicle bone.
shaft of the femur:
Cylindrically shaped region that forms the central portion of the femur.
shaft of the fibula:
Elongated, slender portion located between the expanded ends of the fibula.
shaft of the humerus:
Narrow, elongated, central region of the humerus.
shaft of the radius:
Narrow, elongated, central region of the radius.
shaft of the tibia:
Triangular, central portion of the tibia.
shaft of the ulna:
Narrow, elongated, central region of the ulna.
short bone:
Cube-shaped bone that is approximately equal in length, width, and thickness; provides limited motion.
short reflex:
Reflex arc that does not include any components of the central nervous system.
shunt:
Circulatory shortcut that diverts the flow of blood from one region to another.
sigmoid colon:
End portion of the colon, which terminates at the rectum.
simple columnar epithelium:
Tissue that consists of a single layer of columnlike cells; promotes secretion and absorption in tissues and organs.
simple cuboidal epithelium:
Tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules.
simple squamous epithelium:
Tissue that consists of a single layer of flat, scalelike cells; promotes diffusion and filtration across surfaces.
sinoatrial (SA) node:
Known as the pacemaker, a specialized clump of myocardial conducting cells located in the superior portion of the right atrium that has the highest inherent rate of depolarization that then spreads throughout the heart.
sinusoid capillary:
Rarest type of capillary, which has extremely large intercellular gaps in the basement membrane in addition to clefts and fenestrations; found in areas such as the bone marrow and liver, where passage of large molecules occurs.
sinus rhythm:
Normal electrical pattern followed by contraction of the heart.
sister chromatid:
One of a pair of identical chromosomes, formed during DNA replication.
skeletal muscle:
Striated, multinucleated muscle that requires signalling from the nervous system to trigger contraction; most skeletal muscles are referred to as voluntary muscles that move bones and produce movement.
skeletal muscle pump:
Effect on increasing blood pressure within veins by compression of the vessel caused by the contraction of nearby skeletal muscle.
skeletal system:
Organ system composed of bones and cartilage that provides for movement, support, and protection.
skeleton:
Bones of the body.
skull:
Bony structure that forms the head, face, and jaws, and protects the brain; consists of 22 bones.
sliding filament model of muscle contraction:
Skeletal muscle fibre contracts as the thin filaments are pulled and then slide past the thick filaments within the fibre’s sarcomeres.
slow oxidative (SO):
Muscle fibre that primarily uses aerobic respiration.
small cardiac vein:
Parallels the right coronary artery and drains blood from the posterior surfaces of the right atrium and ventricle; drains into the coronary sinus, middle cardiac vein, or right atrium.
small intestine:
Section of the alimentary canal where most digestion and absorption occurs.
small motor unit:
Arrangement where a single motor neuron supplies a small number of muscle fibres; permits very fine motor control of the muscle.
smooth ER (SER):
Organelle lacking attached ribosomes that are specialized for lipid synthesis, detoxification, carbohydrate metabolism, and calcium ion storage.
smooth muscle:
Nonstriated, mononucleated muscle in the skin that is associated with hair follicles; assists in moving materials in the walls of internal organs, blood vessels, and internal passageways.
sodium bicarbonate:
Anion released into the small intestine to neutralize the pH of the food from the stomach.
sodium-potassium pump (ATPase):
Cell membrane proteins specialized in moving sodium ions (Na+) out of a cell and potassium ions (K+) into a cell, thus regulating ion concentration on both sides of the cell membrane.
soft palate:
Posterior region of the bottom portion of the nasal cavity that consists of skeletal muscle.
soleus:
Wide, flat muscle deep to the gastrocnemius.
solitary nucleus:
Medullar nucleus that receives taste information from the facial and glossopharyngeal nerves.
solution:
Homogeneous liquid mixture in which a solute is dissolved into molecules within a solvent.
soma (cell body):
In neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites).
somatic cell:
All cells of the body excluding gamete cells.
somatic nervous system (SNS):
Functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes.
somatic reflex:
Reflex involving skeletal muscle as the effector, under the control of the somatic nervous system.
somatosensation:
General senses related to the body, usually thought of as the senses of touch, which would include pain, temperature, and proprioception.
somite:
One of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo.
spatial summation:
Combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential.
specialized receptor cell:
Cell that transduces environmental stimuli into neural signals.
special sense:
Any sensory system associated with a specific organ structure, namely, smell, taste, sight, hearing, and balance.
sperm (also spermatozoon):
Male gamete.
spermatic cord:
Bundle of nerves and blood vessels that supplies the testes; contains ductus deferens.
spermatid:
Immature sperm cells produced by meiosis II of secondary spermatocytes.
spermatogenesis:
Formation of new sperm; occurs in the seminiferous tubules of the testes.
spermatogonia (singular = spermatogonium):
Diploid precursor cells that become sperm.
spermatozoa:
Formed sperm that are the end result of spermiogenesis.
spermiogenesis:
Transformation of spermatids to spermatozoa during spermatogenesis.
S phase:
Stage of the cell cycle during which DNA replication occurs.
sphenoid bone:
Unpaired bone that forms the central base of the skull.
sphenoid sinus:
Air-filled space located within the sphenoid bone; most posterior of the paranasal sinuses.
sphygmomanometer:
Blood pressure cuff attached to a device that measures blood pressure.
spinal accessory nerve:
11th cranial nerve; responsible for contraction of neck muscles.
spinal cavity (vertebral cavity):
Division of the dorsal cavity that houses the spinal cord; also referred to as the vertebral cavity.
spinal cord:
Organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviours.
spinal nerve:
One of 31 nerves connected to the spinal cord.
spine of the scapula:
Prominent ridge passing mediolaterally across the upper portion of the posterior scapular surface.
spinothalamic tract:
Ascending tract of the spinal cord associated with pain and temperature sensations.
spinous process:
Unpaired bony process that extends posteriorly from the vertebral arch of a vertebra.
spiral ganglion:
Location of neuronal cell bodies that transmit auditory information along the eighth cranial nerve.
spleen:
Secondary lymphoid organ that filters pathogens from the blood (white pulp) and removes degenerating or damaged blood cells (red pulp).
splenic artery:
Branch of the celiac trunk; supplies blood to the spleen.
splenius:
Posterior neck muscles.
spongy bone (also cancellous bone):
Trabeculated osseous tissue that supports shifts in weight distribution.
spontaneous depolarization (also prepotential depolarization):
The mechanism that accounts for the autorhythmic property of cardiac muscle; the membrane potential increases as sodium ions diffuse through the always-open sodium ion channels and causes the electrical potential to rise.
squamous suture:
Joint that unites the parietal bone to the squamous portion of the temporal bone on the lateral side of the skull.
stage of exhaustion:
Stage three of the general adaptation syndrome; the body’s long-term response to stress mediated by the hormones of the adrenal cortex.
stage of resistance:
Stage two of the general adaptation syndrome; the body’s continued response to stress after stage one diminishes.
stapes (also stirrup):
Ossicle of the middle ear that is attached to the inner ear.
stem cell:
Cell that is oligo-, multi-, or pluripotent and has the ability to produce additional stem cells rather than becoming further specialized.
stereocilia:
Array of apical membrane extensions in a hair cell that transduce movements when they are bent.
sternal (medial) end of the clavicle:
Medial end of the clavicle that articulates with the manubrium of the sternum.
sternal angle:
Junction line between manubrium and body of the sternum; the site for attachment of the second rib to the sternum.
sternal body:
The elongated, central portion of the sternum.
sternoclavicular joint:
Articulation between the manubrium of the sternum and the sternal end of the clavicle; forms the only bony attachment between the pectoral girdle of the upper limb and the axial skeleton.
sternocleidomastoid:
Major muscle that laterally flexes and rotates the head.
sternum:
Flattened bone located at the centre of the anterior chest.
steroid (also sterol):
Lipid compound composed of four hydrocarbon rings bonded to a variety of other atoms and molecules.
stimulus:
An event in the external or internal environment that registers as activity in a sensory neuron.
stomach:
Alimentary canal organ that contributes to chemical and mechanical digestion of food from the esophagus before releasing it, as chyme, to the small intestine.
straight sinus:
Enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and flows into the left or right transverse sinus.
stratified columnar epithelium:
Tissue that consists of two or more layers of columnlike cells, contains glands, and is found in some ducts.
stratified cuboidal epithelium:
Tissue that consists of two or more layers of cube-shaped cells, found in some ducts.
stratified squamous epithelium:
Tissue that consists of multiple layers of cells, with the most apical being flat scalelike cells; protects surfaces from abrasion.
stratum basale:
Deepest layer of the epidermis, made of epidermal stem cells.
stratum basalis:
Part of the lamina propria adjacent to the myometrium; does not shed during menses.
stratum corneum:
Most superficial layer of the epidermis.
stratum functionalis:
Contains the glandular portion of the lamina propria and the endothelial tissue that lines the uterine lumen.
stratum granulosum:
Layer of the epidermis superficial to the stratum spinosum.
stratum lucidum:
Layer of the epidermis between the stratum granulosum and stratum corneum, found only in thick skin covering the palms, soles of the feet, and digits.
stratum spinosum:
Layer of the epidermis superficial to the stratum basale, characterized by the presence of desmosomes.
stress-relaxation response:
Relaxation of smooth muscle tissue after being stretched.
stretch receptors:
Monitor the stretching of tendons, muscles, and the components of joints.
stretch reflex:
Response to activation of the muscle spindle stretch receptor that causes contraction of the muscle to maintain a constant length.
striation:
Alignment of parallel actin and myosin filaments, which form a banded pattern.
stroke volume (SV):
Amount of blood pumped by each ventricle per contraction; also the difference between EDV and ESV.
styloid process:
Downward projecting, elongated bony process located on the inferior aspect of the skull.
styloid process of the radius:
Pointed projection located on the lateral end of the distal radius.
styloid process of the ulna:
Short, bony projection located on the medial end of the distal ulna.
subarachnoid space:
Space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae.
subclavian artery:
Right subclavian arises from the brachiocephalic artery, whereas the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system.
subclavian vein:
Located deep in the thoracic cavity; becomes the axillary vein as it enters the axillary region; drains the axillary and smaller local veins near the scapular region; leads to the brachiocephalic vein.
subclavius:
Muscle that stabilizes the clavicle during movement.
subcortical nucleus:
All the nuclei beneath the cerebral cortex, including the basal nuclei and the basal forebrain.
sublingual gland:
One of a pair of major salivary glands located beneath the tongue.
submandibular gland:
One of a pair of major salivary glands located in the floor of the mouth.
submodality:
Specific sense within a broader major sense, such as sweet as a part of the sense of taste or colour as a part of vision.
submucosa:
Layer of dense connective tissue in the alimentary canal wall that binds the overlying mucosa to the underlying muscularis.
submucosal plexus (plexus of Meissner):
Nerve supply that regulates activity of glands and smooth muscle.
subpubic angle:
Inverted V-shape formed by the convergence of the right and left ischiopubic rami; this angle is greater than 80 degrees in females and less than 70 degrees in males.
subscapular fossa:
Broad depression located on the anterior (deep) surface of the scapula.
subscapularis:
Muscle that originates on the anterior scapula and medially rotates the arm.
subscapular vein:
Drains blood from the subscapular region and leads to the axillary vein.
substantia nigra pars reticulata:
Nuclei within the basal nuclei that serve as an output centre of the nuclei; part of the motor pathway.
substrate:
Reactant in an enzymatic reaction.
subthalamus:
Nucleus within the basal nuclei that is part of the indirect pathway.
sucrase:
Brush border enzyme that breaks down sucrose into glucose and fructose.
sudoriferous gland:
Sweat gland.
sulcus (plural = sulci):
Fat-filled groove visible on the surface of the heart; coronary vessels are also located in these areas.
summate:
To add together, as in the cumulative change in postsynaptic potentials toward reaching threshold in the membrane, either across a span of the membrane or over a certain amount of time.
superficial:
Describes a position nearer to the surface of the body.
superior:
Describes a position above or higher than another part of the body proper; also referred to as cranial.
superior articular process:
Bony process that extends upward from the vertebral arch of a vertebra and articulates with the inferior articular process of the next higher vertebra.
superior articular process of the sacrum:
Paired processes that extend upward from the sacrum to articulate (join) with the inferior articular processes from the L5 vertebra.
superior cervical ganglion:
One of the paravertebral ganglia of the sympathetic system that projects to the head.
superior colliculus:
Structure in the midbrain that combines visual, auditory, and somatosensory input to coordinate spatial and topographic representations of the three sensory systems.
superior mesenteric ganglion:
One of the collateral ganglia of the sympathetic system that projects to the digestive system.
superior nasal concha:
Smallest and most superiorly located of the nasal conchae; formed by the ethmoid bone.
superior orbital fissure:
Irregularly shaped opening between the middle cranial fossa and the posterior orbit.
superior pubic ramus:
Narrow segment of bone that passes laterally from the pubic body to join the ilium.
superior rotation:
Movement of the scapula during upper limb abduction in which the glenoid cavity of the scapula moves in an upward direction as the medial end of the scapular spine moves in a downward direction.
superior sagittal sinus:
Enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein.
superior vena cava:
Large systemic vein that returns blood to the heart from the superior portion of the body.
supinated position:
Forearm position in which the palm faces anteriorly (anatomical position).
supination:
Forearm motion that moves the palm of the hand from the palm backward to the palm forward position.
supinator:
Muscle that moves the palm and forearm anteriorly.
supine:
Face-up.
supplemental motor area:
Cortical area anterior to the primary motor cortex that is responsible for planning movements.
supportive connective tissue:
Type of connective tissue that provides strength to the body and protects soft tissue.
suprahyoid muscles:
Neck muscles that are superior to the hyoid bone.
supraorbital foramen:
Opening located on the anterior skull, at the superior margin of the orbit.
suprascapular notch:
Small notch located along the superior border of the scapula, medial to the coracoid process.
supraspinatus:
Muscle that abducts the arm.
supraspinous fossa:
Narrow depression located on the posterior scapula, superior to the spine.
surgical neck:
Region of the humerus where the expanded, proximal end joins with the narrower shaft.
suspension:
Liquid mixture in which particles distributed in the liquid settle out over time.
suspensory ligaments:
Bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis.
suture:
Fibrous joint that connects the bones of the skull (except the mandible); an immobile joint (synarthrosis).
sweat gland:
Type of gland found in the dermis that secretes sweat through a duct to cool the body.
sympathetic chain ganglia:
Autonomic ganglia in a chain along the anterolateral aspect of the vertebral column that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system.
sympathetic division:
Division of the autonomic nervous system associated with the fight-or-flight response.
sympathetic nervous system:
Branch of the autonomic nervous system that mediates the body’s involuntary response to stress, danger, or intense physical activity.
symphysis:
Type of cartilaginous joint where the bones are joined by fibrocartilage.
symporters:
Secondary active transporters that move two substances in the same direction.
synapse:
Narrow junction across which a chemical signal passes from one neuron to the next, initiating a new electrical signal in the target cell.
synaptic cleft:
Small gap between cells in a chemical synapse where a neurotransmitter diffuses from the presynaptic element to the postsynaptic element.
synaptic end bulb:
Swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse.
synarthrosis:
Immobile or nearly immobile joint.
synchondrosis:
Type of cartilaginous joint where the bones are joined by hyaline cartilage.
syncytiotrophoblast:
Superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall.
syndesmosis:
Type of fibrous joint in which two separated, parallel bones are connected by an interosseous membrane.
synergist:
Muscle whose contraction helps a prime mover in an action.
synostosis:
Site at which adjacent bones or bony components have fused together.
synovial fluid:
Thick, lubricating fluid that fills the interior of a synovial joint.
synovial joint:
Joint at which the articulating surfaces of the bones are located within a joint cavity formed by an articular capsule.
synovial membrane:
Connective tissue membrane that lines the cavities of freely movable joints, producing synovial fluid for lubrication.
synthesis reaction:
Type of anabolic reaction in which two or more atoms or molecules bond, resulting in the formation of a larger molecule.
systemic anatomy:
Study of the structures that contribute to specific body systems.
systemic circuit:
Provides blood rich in oxygen to the body’s tissues, then returns the less oxygenated blood to the heart.
systemic edema:
Increased fluid retention in the interstitial spaces and cells of the body; can be seen as swelling over large areas of the body, particularly the lower extremities.
systemic nerve:
Nerve in the periphery distal to a nerve plexus or spinal nerve.
systole:
Period of time when the heart muscle is contracting.
systolic pressure:
Larger number recorded when measuring arterial blood pressure; represents the maximum value following ventricular contraction.
talus:
Tarsal bone that articulates superiorly with the tibia and fibula at the ankle joint; also articulates inferiorly with the calcaneus bone and anteriorly with the navicular bone.
target effector:
Organ, tissue, or gland that will respond to the control of an autonomic or somatic or endocrine signal.
target heart rate:
Range in which both the heart and the lungs receive the maximum benefit from an aerobic workout.
tarsal bone:
One of the seven bones that make up the posterior foot; includes the calcaneus, talus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform bones.
taste buds:
Structures within a papilla on the tongue that contain gustatory receptor cells.
T cell:
Lymphocyte that acts by secreting molecules that regulate the immune system or by causing the destruction of foreign cells, viruses, and cancer cells.
T cell–dependent antigen:
Antigen that binds to B cells, which requires signals from T cells to make antibody.
T cell–independent antigen:
Binds to B cells, which do not require signals from T cells to make antibody.
tectorial membrane:
Component of the organ of Corti that lies over the hair cells, into which the stereocilia are embedded.
tectospinal tract:
Extrapyramidal connections between the superior colliculus and spinal cord.
telophase:
Final stage of mitosis (and meiosis), preceding cytokinesis, characterized by the formation of two new daughter nuclei.
temporal bone:
Paired bones that form the lateral, inferior portions of the skull, with squamous, mastoid, and petrous portions.
temporal fossa:
Shallow space on the lateral side of the skull, above the level of the zygomatic arch.
temporalis:
Muscle that retracts the mandible.
temporal lobe:
Region of the cerebral cortex directly beneath the temporal bone of the cranium.
temporal summation:
Combination of graded potentials at the same location on a neuron, resulting in a strong signal from one input.
tendon:
Dense connective tissue structure that anchors a muscle to bone.
tendon (Golgi) stretch organs:
Transduce the stretch levels of tendons.
tendon sheath:
Connective tissue that surrounds a tendon at places where the tendon crosses a joint; contains a lubricating fluid to prevent friction and allow smooth movements of the tendon.
tenia coli:
One of three smooth muscle bands that make up the longitudinal muscle layer of the muscularis in all of the large intestine except the terminal end.
tensor fascia lata:
Muscle that flexes and abducts the thigh.
teres major:
Muscle that extends the arm and assists in adduction and medial rotation of it.
teres minor:
Muscle that laterally rotates and extends the arm.
terminal bronchioles:
Smallest airways that lead to the structures of gas exchange.
terminal ganglia:
Ganglia of the parasympathetic division of the autonomic system, which are located near or within the target effector, the latter also known as intramural ganglia.
terminal ganglion:
Autonomic ganglia that are near or within the walls of organs and are responsible for contributing to homeostatic mechanisms of the autonomic nervous system.
tertiary follicles (also antral follicles):
Ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum.
testes (singular = testis):
Male gonads.
testosterone:
Steroid hormone secreted by the testes and important in the maturation of sperm cells, growth and development of the reproductive system, and development of secondary sex characteristics.
tetanus:
A continuous fused contraction.
Th1 cells:
Cells that secrete cytokines that enhance the activity of macrophages and other cells.
Th2 cells:
Cells that secrete cytokines that induce B cells to differentiate into antibody-secreting plasma cells.
thalamus:
Major region of the diencephalon that is responsible for relaying information between the cerebrum and the hindbrain, spinal cord, and periphery.
theca cells:
Estrogen-producing cells in a maturing ovarian follicle.
thermoneutral:
External temperature at which the body does not expend any energy for thermoregulation, about 29°C.
thermoreceptor:
Type of sensory receptor capable of transducing temperature stimuli into neural action potentials.
thermoregulation:
Process of regulating the temperature of the body.
thick filament:
The thick myosin strands and their multiple heads projecting from the centre of the sarcomere toward, but not all the way to, the Z discs.
thigh:
Portion of the lower limb located between the hip and knee joints.
thin filament:
Thin strands of actin and its troponin-tropomyosin complex projecting from the Z discs toward the centre of the sarcomere.
third ventricle:
Portion of the ventricular system that is in the region of the diencephalon.
thoracic aorta:
Portion of the descending aorta superior to the aortic hiatus.
thoracic cage:
Consists of 12 pairs of ribs and the sternum.
thoracic cavity:
Division of the anterior (ventral) cavity that houses the heart, lungs, esophagus, and trachea.
thoracic curve:
Anteriorly concave curvature of the thoracic vertebral column region; a primary curve of the vertebral column.
thoracic duct:
Large duct that drains lymph from the lower limbs, left thorax, left upper limb, and the left side of the head.
thoracic vertebrae:
12 vertebrae numbered T1–T12 that are located in the thoracic region (upper back) of the vertebral column.
thoracic wall compliance:
Ability of the thoracic wall to stretch while under pressure.
thoracolumbar system:
Alternate name for the sympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in the lateral horn of the thoracic.
thoroughfare channel:
Continuation of the metarteriole that enables blood to bypass a capillary bed and flow directly into a venule, creating a vascular shunt.
threshold:
Membrane voltage at which an action potential is initiated.
thrombin:
Enzyme essential for the final steps in formation of a fibrin clot.
thrombocytes:
Platelets, one of the formed elements of blood that consists of cell fragments broken off from megakaryocytes.
thrombocytopenia:
Condition in which there are too few platelets, resulting in abnormal bleeding (hemophilia).
thrombocytosis:
Condition in which there are too many platelets, resulting in abnormal clotting (thrombosis).
thrombopoietin:
Hormone secreted by the liver and kidneys that prompts the development of megakaryocytes into thrombocytes (platelets).
thymocyte:
Immature T cell found in the thymus.
thymosins:
Hormones produced and secreted by the thymus that play an important role in the development and differentiation of T cells.
thymus:
Organ involved in the development and maturation of T cells; particularly active during infancy and childhood.
thyroid cartilage:
Largest piece of cartilage that makes up the larynx and consists of two lamine.
thyroid gland:
Large endocrine gland responsible for the synthesis of thyroid hormones.
thyroid-stimulating hormone (TSH):
Anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (also called thyrotropin).
thyroxine (also tetraiodothyronine, T4):
Amino acid–derived thyroid hormone that is more abundant but less potent than T3 and often converted to T3 by target cells.
tibia:
Shin bone; the large, weight-bearing bone located on the medial side of the leg.
tibial collateral ligament:
Extrinsic ligament of knee joint that spans from the medial epicondyle of the femur to the medial tibia; resists hyperextension and rotation of extended knee.
tibialis anterior:
Muscle located on the lateral surface of the tibia.
tibial nerve:
Systemic nerve of the posterior leg that begins as part of the sciatic nerve.
tibial tuberosity:
Elevated area on the anterior surface of the proximal tibia.
tidal volume (TV):
Amount of air that normally enters the lungs during quiet breathing.
tight junction:
Forms an impermeable barrier between cells that blocks hydrophilic ions or molecules.
tissue:
Group of similar or closely related cells that act together to perform a specific function.
tissue factor:
Protein thromboplastin, which initiates the extrinsic pathway when released in response to tissue damage.
tissue membrane:
Thin layer or sheet of cells that covers the outside of the body, organs, internal passageways, and the lining of joint cavities.
T lymphocytes (also T cells):
Lymphocytes that provide cellular-level immunity by physically attacking foreign or diseased cells.
tongue:
Accessory digestive organ of the mouth, the bulk of which is composed of skeletal muscle.
tonicity:
A measure of a solution’s ability to change the volume of cells by altering their water content.
tonsils (palatine, pharyngeal, and lingual):
Lymphoid nodules associated with the nasopharynx.
topographical:
Relating to positional information.
total dead space:
Sum of the anatomical dead space and alveolar dead space.
total lung capacity (TLC):
Total amount of air that can be held in the lungs; sum of TV, ERV, IRV, and RV.
total pressure:
Sum of all the partial pressures of a gaseous mixture.
totipotent stem cell:
Embryonic stem cell that is capable of differentiating into any and all cells of the body, enabling the full development of an organism.
trabeculae (singular = trabecula):
Spikes or sections of the latticelike matrix in spongy bone.
trabeculae carneae:
Ridges of muscle covered by endocardium located in the ventricles.
trachea:
Tube composed of cartilaginous rings and supporting tissue that connects the lung bronchi and the larynx; provides a route for air to enter and exit the lung.
trachealis muscle:
Smooth muscle located in the fibroelastic membrane of the trachea.
tract:
Bundle of axons in the central nervous system having the same function and point of origin.
transcription:
Process of producing an mRNA molecule that is complementary to a particular gene of DNA.
transduction:
Process of changing an environmental stimulus into the electrochemical signals of the nervous system.
transferrin:
Plasma protein that binds reversibly to iron and distributes it throughout the body.
transfer RNA (tRNA):
Molecules of RNA that serve to bring amino acids to a growing polypeptide strand and properly place them into the sequence.
transient ischemic attack (TIA):
Temporary loss of neurological function caused by a brief interruption in blood flow; also known as a ministroke.
transitional epithelium:
Form of stratified epithelium found in the urinary tract, characterized by an apical layer of cells that change shape in response to the presence of urine.
translation:
Process of producing a protein from the nucleotide sequence code of an mRNA transcript.
transpulmonary pressure:
Pressure difference between the intrapleural and intra-alveolar pressures.
transverse colon:
Part of the colon between the ascending colon and the descending colon.
transverse foramen:
Opening found only in the transverse processes of cervical vertebrae.
transverse plane:
Two-dimensional, horizontal plane that divides the body or organ into superior and inferior portions.
transverse process:
Paired bony process that extends laterally from the vertebral arch of a vertebra.
transversus abdominis:
Deep layer of the abdomen that has fascicles arranged transversely around the abdomen.
trapezius:
Muscle that stabilizes the upper part of the back.
treppe:
Stepwise increase in contraction tension.
tri:
Three.
triad:
A grouping of one T-tubule and two terminal cisternae.
tricarboxylic acid cycle (TCA):
Also called the Krebs cycle or the citric acid cycle; converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules.
triceps brachii:
Three-headed muscle that extends the forearm.
tricuspid valve:
Term used most often in clinical settings for the right atrioventricular valve.
trigeminal nerve:
Fifth cranial nerve; responsible for cutaneous sensation of the face and contraction of the muscles of mastication.
triglyceride:
Lipid compound composed of a glycerol molecule bonded with three fatty acid chains.
trigone:
Area at the base of the bladder marked by the two ureters in the posterior-lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle.
triiodothyronine (also T3):
Amino acid–derived thyroid hormone that is less abundant but more potent than T4.
trimester:
Division of the duration of a pregnancy into three 3-month terms.
trochlea:
Pulley-shaped region located medially at the distal end of the humerus; articulates at the elbow with the trochlear notch of the ulna.
trochlear nerve:
Fourth cranial nerve; responsible for contraction of one of the extraocular muscles.
trochlear notch:
Large, C-shaped depression located on the anterior side of the proximal ulna; articulates at the elbow with the trochlea of the humerus.
trophoblast:
Fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes.
tropomyosin:
Regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin.
troponin:
Regulatory protein that binds to actin, tropomyosin, and calcium.
true labour:
Regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time.
true ribs:
Vertebrosternal ribs 1–7, which attach via their costal cartilage directly to the sternum.
true vocal cord:
One of the pair of folded, white membranes that have a free inner edge that oscillates as air passes through to produce sound.
trunk:
Large vessel that gives rise to smaller vessels.
trypsin:
Pancreatic enzyme that activates chymotrypsin and digests protein.
trypsinogen:
Proenzyme form of trypsin.
T-tubule:
Projection of the sarcolemma into the interior of the cell.
tubercle of the rib:
Small bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebra.
tubuloglomerular feedback:
Feedback mechanism involving the JGA; macula densa cells monitor Na+ concentration in the terminal portion of the ascending loop of Henle and act to cause vasoconstriction or vasodilation of afferent and efferent arterioles to alter GFR.
tunica externa (also tunica adventitia):
Outermost layer or tunic of a vessel (except capillaries).
tunica intima (also tunica interna):
Innermost lining or tunic of a vessel.
tunica media:
Middle layer or tunic of a vessel (except capillaries).
T wave:
Component of the electrocardiogram that represents the repolarization of the ventricles.
twitch:
Single contraction produced by one action potential.
tympanic membrane:
Ear drum.
type I alveolar cell:
Squamous epithelial cells that are the major cell type in the alveolar wall; highly permeable to gases.
type II alveolar cell:
Cuboidal epithelial cells that are the minor cell type in the alveolar wall; secrete pulmonary surfactant.
ulna:
Bone located on the medial side of the forearm.
ulnar artery:
Formed at the bifurcation of the brachial artery; parallels the ulna; gives off smaller branches until it reaches the carpal region, where it fuses with the radial artery to form the superficial and deep palmar arches; supplies blood to the lower arm and carpal region.
ulnar collateral ligament:
Intrinsic ligament on the medial side of the elbow joint; spans from the medial epicondyle of the humerus to the medial ulna.
ulnar nerve:
Systemic nerve of the arm located close to the ulna, a bone of the forearm.
ulnar tuberosity:
Roughened area located on the anterior, proximal ulna inferior to the coronoid process.
ulnar vein:
Parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein.
umbilical arteries:
Pair of vessels that runs within the umbilical cord and carries fetal blood low in oxygen and high in waste to the placenta for exchange with maternal blood.
umbilical cord:
Connection between the developing conceptus and the placenta; carries deoxygenated blood and waste from the fetus and returns nutrients and oxygen from the mother.
umbilical vein:
Single vessel that originates in the placenta and runs within the umbilical cord, carrying oxygen- and nutrient-rich blood to the fetal heart.
uniaxial joint:
Type of diarthrosis; joint that allows for motion within only one plane (one axis).
unipennate:
Pennate muscle that has fascicles located on one side of the tendon.
unipolar:
Shape of a neuron that has only one process that includes both the axon and dendrite.
universal donor:
Individual with type O− blood.
universal recipient:
Individual with type AB+ blood.
upper esophageal sphincter:
Skeletal muscle sphincter that regulates food movement from the pharynx to the esophagus.
upper motor neuron:
First neuron in the motor command pathway with its cell body in the cerebral cortex; synapses on the lower motor neuron in the spinal cord.
upregulation:
Increase in the number of hormone receptors, typically in response to chronically reduced levels of a hormone.
urea cycle:
Process that converts potentially toxic nitrogen waste into urea that can be eliminated through the kidneys.
urethra:
Transports urine from the bladder to the outside environment.
urinalysis:
Analysis of urine to diagnose disease.
uterine tubes (also fallopian tubes or oviducts):
Ducts that facilitate transport of an ovulated oocyte to the uterus.
uterus:
Muscular hollow organ in which a fertilized egg develops into a fetus.
utricle:
Structure of the inner ear responsible for transducing linear acceleration in the horizontal plane.
uvula:
Fleshy bead of tissue that drops down from the centre of the posterior edge of the soft palate.
vagina:
Tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby.
vagus nerve:
10th cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities.
valence shell:
Outermost electron shell of an atom.
Valsalva’s maneuver:
Voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation.
valve:
In the cardiovascular system, a specialized structure located within the heart or vessels that ensures one-way flow of blood.
varicosity:
Structure of some autonomic connections that is not a typical synaptic end bulb, but a string of swellings along the length of a fibre that makes a network of connections with the target effector.
vasa recta:
Branches of the efferent arterioles that parallel the course of the loops of Henle and are continuous with the peritubular capillaries; with the glomerulus, form a portal system.
vasa vasorum:
Small blood vessels located within the walls or tunics of larger vessels that supply nourishment to and remove wastes from the cells of the vessels.
vascular shock:
Type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically.
vascular shunt:
Continuation of the metarteriole and thoroughfare channel that allows blood to bypass the capillary beds to flow directly from the arterial to the venous circulation.
vascular spasm:
Initial step in hemostasis, in which the smooth muscle in the walls of the ruptured or damaged blood vessel contracts.
vascular tone:
Contractile state of smooth muscle in a blood vessel.
vascular tunic:
Middle layer of the eye primarily composed of connective tissue with a rich blood supply.
vasoconstriction:
Constriction of the smooth muscle of a blood vessel, resulting in a decreased vascular diameter.
vasodilation:
Relaxation of the smooth muscle in the wall of a blood vessel, resulting in an increased vascular diameter.
vasomotion:
Irregular, pulsating flow of blood through capillaries and related structures.
vasomotor centres:
Control vessel tone or contraction of the smooth muscle in the tunica media.
vasomotor nerves:
Preganglionic sympathetic fibres that cause the constriction of blood vessels in response to signals from the cardiovascular centre.
vastus intermedius:
Quadricep muscle that is between the vastus lateralis and vastus medialis and is deep to the rectus femoris.
vastus lateralis:
Quadricep muscle on the lateral aspect of the thigh.
vastus medialis:
Quadricep muscle on the medial aspect of the thigh.
vein:
Blood vessel that conducts blood toward the heart.
vein valves:
Assist the unidirectional flow of blood toward the heart; particularly those of the limbs.
venous reserve:
Volume of blood contained within systemic veins in the integument, bone marrow, and liver that can be returned to the heart for circulation if needed.
ventilation:
Movement of air into and out of the lungs; consists of inspiration and expiration.
ventral:
Describes the front or direction toward the front of the body; also referred to as anterior.
ventral cavity:
Larger body cavity located anterior to the posterior (dorsal) body cavity; includes the serous membrane-lined pleural cavities for the lungs, pericardial cavity for the heart, and peritoneal cavity for the abdominal and pelvic organs; also referred to as the anterior body cavity.
ventral respiratory group (VRG):
Region of the medulla oblongata that stimulates the contraction of the accessory muscles involved in respiration to induce forced inspiration and expiration.
ventral stream:
Connections between cortical areas from the occipital lobe to the temporal lobe that are responsible for the identification of visual stimuli.
ventricle (brain):
Central cavity within the brain where CSF is produced and circulates.
ventricle (heart):
One of the primary pumping chambers of the heart located in the lower portion of the heart; the left ventricle is the major pumping chamber on the lower left side of the heart that ejects blood into the systemic circuit via the aorta and receives blood from the left atrium; the right ventricle is the major pumping chamber on the lower right side of the heart that ejects blood into the pulmonary circuit via the pulmonary trunk and receives blood from the right atrium.
ventricular ejection phase:
Second phase of ventricular systole during which blood is pumped from the ventricle.
venule:
Small vessel leading from the capillaries to veins.
vernix caseosa:
Waxy, cheese-like substance that protects the delicate fetal skin until birth.
vertebra:
Individual bone in the neck and back regions of the vertebral column.
vertebral (spinal) canal:
Bony passageway within the vertebral column for the spinal cord that is formed by a series of individual vertebral foramina.
vertebral arch:
Bony arch formed by the posterior portion of each vertebra that surrounds and protects the spinal cord.
vertebral arteries:
Arteries that ascend along either side of the vertebral column through the transverse foramina of the cervical vertebrae and enter the cranium through the foramen magnum.
vertebral body:
The anterior portion of each vertebra; the part that supports body weight.
vertebral column:
Entire sequence of bones that extend from the skull to the tailbone.
vertebral foramen:
Opening associated with each vertebra, defined by the vertebral arch that provides passage for the spinal cord.
vesicle:
Membrane-bound structure that contains materials within or outside of the cell.
vestibular apparatus:
Component of the vestibular system that contains the hair cell with stereocilia responsible for senses, head position, head movement, and whether our bodies are in motion.
vestibular fold:
Part of the folded region of the glottis composed of mucous membrane; supports the epiglottis during swallowing.
vestibular ganglion:
Location of neuronal cell bodies that transmit equilibrium information along the eighth cranial nerve.
vestibular nuclei:
Targets of the vestibular component of the eighth cranial nerve.
vestibule:
In the ear, the portion of the inner ear responsible for the sense of equilibrium.
vestibulocochlear nerve (auditory):
Eighth cranial nerve; responsible for the sensations of hearing and balance.
vestibulo-ocular reflex (VOR):
Reflex based on connections between the vestibular system and the cranial nerves of eye movements that ensures images are stabilized on the retina as the head and body move.
vestibulospinal tract:
Extrapyramidal connections between the vestibular nuclei in the brain stem and spinal cord that modulate movement and contribute to balance on the basis of the sense of equilibrium.
villus:
Projection of the mucosa of the small intestine.
visceral branches:
Branches of the descending aorta that supply blood to the viscera.
visceral layer:
Serous membrane that covers the organs (the viscera).
visceral muscle:
Smooth muscle found in the walls of visceral organs.
visceral pericardium (epicardium):
Layer of serous pericardium that is fused to the heart and is part of the heart wall.
visceral peritoneum:
Envelopes the abdominal organs.
visceral pleura:
Innermost layer of the pleura that is superficial to the lungs and extends into the lung fissures.
visceral reflex:
Reflex involving an internal organ as the effector, under the control of the autonomic nervous system.
visceral sense:
Sense associated with the internal organs.
vision:
Special sense of sight based on the transduction of light stimuli.
visual acuity:
Property of vision related to the sharpness of focus, which varies in relation to retinal position.
vital capacity (VC):
Sum of TV, ERV, and IRV, which is all the volumes that participate in gas exchange.
vitamin D:
Compound that aids absorption of calcium and phosphates in the intestine to improve bone health.
vitamins:
Organic compounds required by the body to perform biochemical reactions like metabolism and bone, cell, and tissue growth.
vitreous humour:
Viscous fluid that fills the posterior chamber of the eye.
voltage-gated channel:
Ion channel that opens because of a change in the charge distributed across the membrane where it is located.
voltage-gated sodium channels:
Membrane proteins that open sodium channels in response to a sufficient voltage change and initiate and transmit the action potential as Na+ enters through the channel.
voluntary phase:
Initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx.
vomer bone:
Unpaired bone that forms the inferior and posterior portions of the nasal septum.
vulva:
External female genitalia.
wave summation:
Addition of successive neural stimuli to produce greater contraction.
white blood cells (WBCs; also leukocytes):
One of the formed elements of blood that provides defence against disease agents and foreign materials.
white matter:
Regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin.
white pulp:
Splenic nodule area that resembles the lymphoid follicles of the lymph nodes.
white rami communicantes (singular = ramus communicans):
Myelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the preganglionic sympathetic fibre.
withdrawal reflex:
From a painful stimulus only requires the sensory fibre that enters the spinal cord and the motor neuron that projects to a muscle.
working memory:
Function of the prefrontal cortex to maintain a representation of information that is not in the immediate environment.
xiphoid process:
Small process that forms the inferior tip of the sternum.
yellow marrow:
Connective tissue in the interior cavity of a bone where fat is stored.
yolk sac:
Membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure.
Z discs:
Three-dimensional cylinder-like arrangement of sarcomere.
zona fasciculata:
Intermediate region of the adrenal cortex that produces hormones called glucocorticoids.
zona glomerulosa:
Most superficial region of the adrenal cortex; produces the hormones collectively referred to as mineralocorticoids.
zona pellucida:
Thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur.
zona reticularis:
Deepest region of the adrenal cortex; produces the steroid sex hormones called androgens.
zonule fibres:
Fibrous connections between the ciliary body and the lens.
zygomatic arch:
Elongated, freestanding arch on the lateral skull, formed anteriorly by the temporal process of the zygomatic bone.
zygomatic bone:
Cheekbone; paired bones that contribute to the lateral orbit and anterior zygomatic arch.
zygote:
Fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines.

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