Glossary: Human Body Systems
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A
Abdominal Cavity: The body cavity in mammals that primarily houses parts of the
digestive, excretory, and reproductive systems. It is separated from the thoracic cavity
by the diaphragm.
Abduction: Movement away from the midline of the body.
Accommodation: The automatic adjustment of the eye for seeing at different distances
affected chiefly by changes in the convexity of the crystalline lens.
Actin: A contractile protein that is part of the thin filaments in muscle fibers.
Action Potential: A momentary reversal in electrical potential across a plasma
membrane (as of a nerve cell or muscle fiber) that occurs when a cell has been
activated by a stimulus.
Adduction: Movement toward the midline off the body.
Adenosine Triphosphate (ATP): An adenine-containing nucleoside triphosphate that
releases free energy when its phosphate bonds are hydrolyzed. This energy is used to
drive endergonic reactions in the cell.
Adipose Tissue: Connective tissue in which fat is stored and which has the cells
distended by droplets of fat.
Adrenal Glands: Hormone-producing glands located superior to the kidneys; each
consists of a medulla and a cortex.
Aerobic: Containing oxygen; referring to an organism, environment, or cellular process
that requires oxygen.
Afferent neurons: Nerve cells that carry impulses towards the central nervous system.
Agarose: A polysaccharide obtained from seaweed that is used as the supporting
medium in gel electrophoresis.
Agglutination: Clumping of microorganisms or blood cells, typically due to an antigenantibody reaction.
Aldosterone: A mineralcortocoid produced by the adrenal cortex that promotes sodium
and water reabsorption by the kidneys and potassium excretion in urine.
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Alveoli: Terminal air sacs that constitute the gas exchange surface of the lungs.
Anabolic Steroids: Any of a group of usually synthetic hormones that are derivatives of
testosterone, are used medically especially to promote tissue growth, and are
sometimes abused by athletes to increase the size and strength of their muscles and
improve endurance.
Anabolism: Synthetic, energy-requiring reactions whereby small molecules are built up
into larger ones.
Anaerobic: Lacking oxygen; referring to an organism, environment, or cellular process
that lacks oxygen and may be poisoned by it.
Anatomy: The structure or study of structure of the body and the relation of its parts to
each other.
Anterior: Situated toward the front of the body.
Antibody: An antigen-binding immunoglobulin, produced by B cells, that functions as
the effector in an immune response.
Antidiuretic Hormone (ADH): Hormone produced by the neurosecretory cells in the
hypothalamus that stimulates water reabsorption from kidney tubule cells into the blood
and vasoconstriction of arterioles.
Antigen: A foreign macromolecule that does not belong to the host organism and elicits
and immune response.
Aorta: The large arterial trunk that carries blood from the heart to be distributed by
branch arteries through the body.
Appendicular Skeleton: Bones of the limbs and limb girdles that are attached to the
axial skeleton.
Arteriole: Any of the small terminal twigs of an artery that ends in capillaries.
Artery: Any of the tubular branching muscular- and elastic-walled vessels that carry
blood from the heart through the body.
Articular Cartilage: Hyaline cartilage attached to articular bone surfaces.
Articulation: The action or manner in which the parts come together at a joint.
Astigmatism: A defect of an optical system (as a lens) causing rays from a point to fail
to meet in a focal point resulting in a blurred and imperfect image.
Atherosclerosis: A cardiovascular disease in which growths called plaques develop on
the inner walls of the arteries, narrowing their inner diameters.
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Atrium: A chamber of the heart that receives blood from the veins and forces it into a
ventricle or ventricles.
Axial Skeleton: The skeleton of the trunk and head.
Axon: A usually long and single nerve-cell process that usually conducts impulses away
from the cell body.
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B
Ball-and-socket Joint: An articulation (as the hip joint) in which the rounded head of
one bone fits into a cuplike cavity of the other and admits movement in any direction.
Basal Metabolic Rate (BMR): The rate at which heat is given off by an organism at
complete rest.
Biometrics: The measurement and analysis of unique physical or behavioral
characteristics (as fingerprint or voice patterns) especially as a means of verifying
personal identity.
Blind Spot: The small circular area in the retina where the optic nerve enters the eye
that is devoid of rods and cones and is insensitive to light.
Blood Doping: A technique for temporarily improving athletic performance in which
oxygen-carrying red blood cells previously withdrawn from an athlete are injected back
just before an event.
Blood Group: One of the classes (as A, B, AB, or O) into which individual vertebrates
and especially human beings or their blood can be separated on the basis of the
presence or absence of specific antigens in the blood -- called also blood type.
Blood Pressure: The hydrostatic force that blood exerts against the wall of a vessel.
B Lymphocyte (B cell): A type of lymphocyte that develops in the bone marrow and
later produces antibodies, which mediate humoral immunity.
Body Mass Index (BMI): A measure of body fat that is the ratio of the weight of the
body in kilograms to the square of its height in meters.
Bolus: A soft mass of chewed food.
Bone Marrow: A soft highly vascular modified connective tissue that occupies the
cavities and cancellous part of most bones and occurs in two forms – yellow and red.
Bone Remodeling: The continuous turnover of bone matrix and mineral that involves
first, an increase in resorption and osteoclast activity, and later, reactive bone formation
by osteoblast activity.
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Brain Stem: The part of the brain composed of the midbrain, pons, and medulla
oblongata and connecting the spinal cord with the forebrain and cerebrum.
Bronchi: Pair of breathing tubes that branch from the trachea into the lungs.
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C
Calcitonin: A polypeptide hormone especially from the thyroid gland that tends to lower
the level of calcium in the blood plasma.
Callus: A growth of new bone tissue in and around a fractured area, ultimately replaced
by mature bone.
Calorie: The amount of heat energy required to raise the temperature of 1 g of water by
1°C. The Calorie (with a capital C), usually used to indicate the energy content of food,
is a kilocalorie.
Capillary: Any of the smallest blood vessels connecting arterioles with venules and
forming networks throughout the body.
Cardiac Muscle: Striated muscle fibers (cells) that form the wall of the heart; stimulated
by the intrinsic conduction system and autonomic motor neurons.
Cardiac Output: The volume of blood ejected from the left side of the heart in one
minute.
Carpal Tunnel Syndrome: A condition caused by compression of the median nerve in
the carpal tunnel and characterized especially by weakness, pain, and disturbances of
sensation in the hand and fingers.
Cartilage: A usually translucent somewhat elastic tissue that composes most of the
skeleton of vertebrate embryos and except for a small number of structures (as some
joints, respiratory passages, and the external ear) is replaced by bone during
ossification in the higher vertebrates.
Case Study: A detailed analysis of a person or group, especially as a model of medical,
psychiatric, psychological, or social phenomena.
Catabolism: Chemical reactions that break down complex organic compounds into
simple ones, with the net release of energy.
Cell: The basic structural and functional unit of all organisms; the smallest structure
capable of performing all of the activities vital to life.
Cellular Respiration: The most prevalent and efficient catabolic pathway for the
production of ATP, in which oxygen is consumed as a reactant along with the organic
fuel.
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Central Nervous System: The part of the nervous system which in vertebrates consists
of the brain and spinal cord, to which sensory impulses are transmitted and from which
motor impulses pass out, and which supervises and coordinates the activity of the entire
nervous system.
Cerebellum: A large dorsally projecting part of the brain concerned especially with the
coordination of muscles and the maintenance of bodily equilibrium, situated between
the brain stem and the back of the cerebrum and formed in humans of two lateral lobes
and a median lobe.
Cerebrum: The dorsal portion, composed of right and left hemispheres, of the
vertebrate forebrain; the integrating center for memory, learning, emotions, and other
highly complex function of the central nervous system.
Circulation: The movement of blood through the vessels of the body that is induced by
the pumping action of the heart and serves to distribute nutrients and oxygen to and
remove waste products from all parts of the body.
Circumduction: A movement at a synovial joint in which the distal end of the bone
moves in a circle while the proximal end remains relatively stable.
Collagen: An insoluble fibrous protein of vertebrates that is the chief constituent of the
fibrils of connective tissue (as in skin and tendons) and of the organic substance of
bones.
Compact Bone: Bone tissue that contains few spaces between osteons; forms the
external portion of all bones and the bulk of the diaphysis (shaft) of long bones.
Cone: Any of the conical photosensitive receptor cells of the vertebrate retina that
function in color vision.
Connective Tissue: Animal tissue that functions mainly to bind and support other
tissues, having a sparse population of cells scattered through an extracellular matrix.
Contract: To shorten and thicken.
Cornea: The transparent part of the coat of the eyeball that covers the iris and pupil and
admits light to the interior.
Coronary Artery: Either of two arteries that arise one from the left and one from the
right side of the aorta immediately above the semilunar valves and supply the tissues of
the heart itself.
Creatine Phosphate: A compound of creatine and phosphoric acid that is found
especially in vertebrate muscle where it is an energy source for muscle contraction.
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D
Deep: Away from the body surface; more internal
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Dendrite: Any of the usually branching protoplasmic processes that conduct impulses
toward the body of a neuron.
Deoxyribonucleic Acid (DNA): A double-stranded, helical nucleic acid molecule
capable of replicating and determining the inherited structure of a cell’s proteins.
Depth Perception: The ability to judge the distance of objects and the spatial
relationship of objects at different distances.
Dermis: The sensitive vascular inner mesodermic layer of the skin.
Diaphragm: A sheet of muscle that forms the bottom wall of the thoracic cavity in
mammals; active in ventilating the lungs.
Diaphysis: The shaft of a long bone.
Digestion: The process of making food absorbable by mechanically and enzymatically
breaking it down into simpler chemical compounds in the alimentary canal.
Digestive System: The bodily system concerned with the ingestion, digestion, and
absorption of food.
Directional Terms: Terms used to explain where one body structure is in relation to
another.
Dislocation: Displacement of a bone from a joint with tearing of ligaments, tendons,
and articular capsules.
Distal: Situated away from the point of attachment or origin or a central point; located
away from the center of the body.
Dorsal: Being or located near, on, or toward the back or posterior part of the human
body.
Dorsiflexion: Bending the foot in the direction of the dorsum (upper surface).
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E
Efferent neurons: Nerve cells that carry impulses away from the central nervous
system.
Elastin: A protein that is similar to collagen and is the chief constituent of elastic fibers.
Electricity: A fundamental form of energy observable in positive and negative forms
that occurs naturally (as in lightning) or is produced (as in a generator) and that is
expressed in terms of the movement and interaction of electrons or ions.
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Endocrine Gland: A gland (as the thyroid or the pituitary) that produces an endocrine
secretion -- called also ductless gland, gland of internal secretion.
Endocrine System: The glands and parts of glands that produce endocrine secretions,
help to integrate and control bodily metabolic activity, and include especially the
pituitary, thyroid, parathyroid, adrenals, islets of Langerhans, ovaries, and testes.
Endomysium: The delicate connective tissue surrounding the individual muscular fibers
within the smallest bundles.
Endorphin: A hormone produced in the brain and anterior pituitary that inhibits pain
perception.
Enzyme: A protein serving as a catalyst, a chemical agent that changes the rate of
reaction without being consumed by the reaction.
Epidermis: The outer nonsensitive and nonvascular layer of the skin of a vertebrate
that overlies the dermis.
Epimysium: The external connective-tissue sheath of a muscle.
Epiphysis: The end of a long bone, usually larger in diameter than the shaft.
Epithelial Tissue: Sheets of tightly packed cells that line organs and body cavities.
Epithelium: A membranous cellular tissue that covers a free surface or lines a tube or
cavity of an animal body and serves especially to enclose and protect the other parts of
the body, to produce secretions and excretions, and to function in assimilation.
Erythrocyte: A mature red blood cell.
Erythropoietin: A hormonal substance that is formed especially in the kidney and
stimulates red blood cell formation.
Esophagus: A muscular tube that in adult humans is about nine inches (23
centimeters) long and passes from the pharynx down the neck between the trachea and
the spinal column and behind the left bronchus where it pierces the diaphragm slightly
to the left of the middle line and joins the cardiac end of the stomach.
Excretion: The disposal of nitrogen-containing waste products of metabolism.
Exocrine Gland: A gland (as a sweat gland, a salivary gland, or a kidney) that releases
a secretion external to or at the surface of an organ by means of a canal or duct.
Extension: An unbending movement around a joint in a limb (as the knee or elbow) that
increases the angle between the bones of the limb at the joint.
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F
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Fascicle: A small bundle or cluster, especially of nerve or muscle fibers.
Femur: The proximal bone of the hind or lower limb that is the longest and largest bone
in the human body; extends from the hip to the knee.
Filtration: In the vertebrate kidney, the extraction of water and small solutes, including
metabolic wastes, from the blood by the nephrons.
First-degree Burn: A mild burn characterized by heat, pain, and reddening of the
burned surface but not exhibiting blistering or charring of tissues.
Flexion: A bending movement around a joint in a limb (as the knee or elbow) that
decreases the angle between the bones of the limb at the joint.
Forensic Anthropology: The branch of physical anthropology in which anthropological
data, criteria, and techniques are used to determine the sex, age, genetic population, or
parentage of skeletal or biological materials in questions of civil or criminal law.
Fracture: The breaking of hard tissue (as bone).
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G
Gallbladder: A membranous muscular sac in which bile from the liver is stored.
Gastrointestinal Tract: The stomach and intestine as a functional unit.
Gel Electrophoresis: The separation of nucleic acids or proteins, on the basis of their
size and electrical charge, by measuring their rate of movement through an electrical
field in a gel.
Gland: A cell, group of cells, or organ of endothelial origin that selectively removes
materials from the blood, concentrates or alters them, and secretes them for further use
in the body or for elimination from the body.
Glomerular Filtration: The first step in urine formation in which substances in blood
pass through the filtration membrane and the filtrate enters the proximal convoluted
tubule of the nephron.
Glomerulus: A ball of capillaries surrounded by Bowman’s capsule in the nephron and
serving as the site of filtration in the vertebrate kidney.
Glucagon: A protein hormone that is produced especially by the pancreatic islets of
Langerhans and that promotes an increase in the sugar content of the blood by
increasing the rate of breakdown of glycogen in the liver.
Glycogen: A highly branched polymer of glucose containing thousands of subunits;
functions as a compact store of glucose molecules in liver and muscle fibers
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Goniometer: An instrument for measuring angles (as of a joint or the skull).
Gyrus: A convoluted ridge between anatomical grooves.
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H
Heart Rate: A measure of cardiac activity usually expressed as number of beats per
minute.
Hinge Joint: Joint between bones (as at the elbow or knee) that permits motion in only
one plane.
Homeostasis: The maintenance of relatively stable internal physiological conditions (as
body temperature or the pH of blood) in higher animals under fluctuating environmental
conditions.
Hormone: Any one of the many circulating chemical signals found in all multicellular
organisms that are formed in specialized cells, travel in body fluids, and coordinate the
various parts of the organism by interacting with target cells.
Humerus: The longest bone of the upper arm or forelimb extending from the shoulder
to the elbow.
Hyaline Cartilage: Translucent bluish white cartilage consisting of cells embedded in
an apparently homogeneous matrix, present in joints and respiratory passages, and
forming most of the fetal skeleton.
Hyperopia: A condition in which visual images come to a focus behind the retina of the
eye and vision is better for distant than for near objects -- called also farsightedness.
Hypothalamus: The ventral part of the vertebrate forebrain; functions in maintaining
homeostasis, especially in coordinating the endocrine and nervous systems; secretes
hormones of the posterior pituitary and releasing factors, which regulate the anterior
pituitary.
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I
Identity: The distinguishing character or personality of an individual
Immunity: A condition of being able to resist a particular disease especially through
preventing development of a pathogenic microorganism or by counteracting the effects
of its products.
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Inferior: Situated below and closer to the feet than another and especially another
similar part of an upright body especially of a human being.
Ingestion: The taking in of foods, liquids, or drugs, by mouth.
Insertion: The attachment of a muscle tendon to a moveable bone or the end opposite
the origin.
Insulin: A vertebrate hormone that lowers blood glucose levels by promoting the uptake
of glucose by most body cells and the synthesis and storage of glycogen in the liver.
Intercostal Muscle: Muscle located between the ribs.
Intervention: Any measure whose purpose is to improve health or alter the course of
disease.
Ion: An atom or group of atoms that carries a positive or negative electric charge as a
result of having lost or gained one or more electrons.
Iris: The opaque muscular contractile diaphragm that is suspended in the aqueous
humor in front of the lens of the eye, is perforated by the pupil and is continuous
peripherally with the ciliary body, has a deeply pigmented posterior surface which
excludes the entrance of light except through the pupil and a colored anterior surface
which determines the color of the eyes.
Isometric Contraction: A muscle contraction in which tension on the muscle increases,
but there is only minimal muscle shortening so that no visible movement is produced.
Isotonic Contraction: Contraction in which the tension remains the same; occurs when
a constant load is moved through the range of motions possible at a joint.
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J
Joint: The point of contact between elements of an animal skeleton whether movable or
rigidly fixed together with the surrounding and supporting parts (as membranes,
tendons, or ligaments).
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K
Keratin: Any of various sulfur-containing fibrous proteins that form the chemical basis of
epidermal tissues (as hair and nails) and are typically not digested by enzymes of the
gastrointestinal tract.
Kidney: One of a pair of vertebrate organs situated in the body cavity near the spinal
column that excrete waste products of metabolism, in humans are bean-shaped organs
about 4½ inches (11½ centimeters) long lying behind the peritoneum in a mass of fatty
tissue, and consist chiefly of nephrons by which urine is secreted, collected, and
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discharged into the pelvis of the kidney whence it is conveyed by the ureter to the
bladder.
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L
Lactic Acid: An organic acid present in blood and muscle tissue as a product of the
anaerobic metabolism of glucose and glycogen.
Large Intestine: The more terminal division of the vertebrate intestine that is wider and
shorter than the small intestine, typically divided into cecum, colon, and rectum, and
concerned especially with the resorption of water and the formation of feces.
Lateral: Of or relating to the side; especially of a body part.
Lens: A curved piece of glass or plastic used singly or combined in eyeglasses or an
optical instrument (as a microscope) for forming an image by focusing rays of light.
Leukocyte: A white blood cell.
Ligament: Dense regular connective tissue that attaches bone to bone.
Limbic System: A group of subcortical structures (as the hypothalamus, the
hippocampus, and the amygdala) of the brain that are concerned especially with
emotion and motivation.
Liver: The largest organ in vertebrate body; performs diverse functions such as
producing bile, preparing nitrogenous wastes for disposal, and detoxifying poisonous
chemicals in the blood.
Lobe: A division of a body organ (as the brain, lungs, or liver) marked off by a fissure on
the surface.
Lungs: Main organs of respiration that lie on either side of the heart in the thoracic
cavity.
Lymph: A usually clear fluid that passes from intercellular spaces of body tissue into the
lymphatic vessels, is discharged into the blood by way of the thoracic duct and right
lymphatic duct, and resembles blood plasma in containing white blood cells and
especially lymphocytes but normally few red blood cells and no platelets.
Lymph Node: Any of the rounded masses of lymphoid tissue that are surrounded by a
capsule of connective tissue, are distributed along the lymphatic vessels, and contain
numerous lymphocytes which filter the flow of lymph passing through the node.
Lymphocyte: Any of the colorless weakly motile cells that originate from stem cells and
differentiate in lymphoid tissue (as of the thymus or bone marrow), that are the typical
cellular elements of lymph, that include the cellular mediators of immunity, and that
constitute 20 to 30 percent of the white blood cells of normal human blood.
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M
Macromolecule: A very large molecule (as of a protein, nucleic acid, or carbohydrate)
built up from smaller chemical structures.
Macrophage: An amoeboid cell that moves through tissue fibers, engulfing bacteria and
dead cells by phagocytosis.
Medial: Lying or extending in the middle; especially of a body part.
Melanin: Any of various black, dark brown, reddish brown, or yellow pigments of animal
or plant structures (as in skin and hair).
Memory Cell: A long-lived lymphocyte that carries the antibody or receptor for a
specific antigen after a first exposure to the antigen and that remains in a less than
mature state until stimulated by a second exposure to the antigen at which time it
mounts a more effective immune response than a cell which has not been exposed
previously.
Metabolism: The totality of an organism’s chemical reactions, consisting of catabolic
and anabolic pathways.
Minute Volume: The volume of air breathed in one minute without conscious effort.
Minute volume = Tidal Volume x (breaths/minute).
Muscle: An organ composed of one of the three types of muscular tissue (skeletal,
cardiac, and smooth), specialized for contraction to produce voluntary and involuntary
movements of parts of the body.
Muscle Fatigue: Inability of muscle to maintain its strength of contraction or tension;
may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup.
Myelin sheath: In a neuron, an insulating coat of cell membrane from Schwann cells
that is interrupted by nodes of Ranvier.
Myofibril: A threadlike structure, extending longitudinally through a muscle fiber (cell)
consisting mainly of think filaments (myosin) and thin filaments (actin, troponin, and
tropomyosin).
Myopia: A condition in which the visual images come to a focus in front of the retina of
the eye because of defects in the refractive media of the eye or of abnormal length of
the eyeball resulting especially in defective vision of distant objects -- called also
nearsightedness.
Myosin: The contractile protein that makes up the thick filaments of muscle fibers.
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N
Nephron: The tubular excretory unit of the vertebrate kidney.
Nerve: A cordlike bundle of neuronal axons and/or dendrites and associated connective
tissue coursing together outside the central nervous system.
Neurologist: A physician skilled in the diagnosis and treatment of disease of the
nervous system.
Neuron: A nerve cell; the fundamental unit of the nervous system, having structure and
properties that allow it to conduct signals by taking advantage of the electrical charge
across its cell membrane.
Neurotransmitter: A substance (as norepinephrine or acetylcholine) that transmits
nerve impulses across a synapse.
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O
Optic Nerve: Either of the pair of sensory nerves that comprise the second pair of
cranial nerves, arise from the ventral part of the diencephalon, form an optic chiasma
before passing to the eye and spreading over the anterior surface of the retina, and
conduct visual stimuli to the brain.
Oral Cavity: The part of the mouth behind the gums and teeth that is bounded above by
the hard and soft palates and below by the tongue and by the mucous membrane
connecting it with the inner part of the mandible.
Origin: The attachment of a muscle tendon to a stationary bone or the end opposite the
insertion.
Osteoblast: A bone-forming cell.
Osteoclast: Any of the large multinucleate cells closely associated with areas of bone
resorption (as in a fracture that is healing).
Osteocyte: Cell that is characteristic of adult bone and is isolated in a lacuna of the
bone substance.
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P
Pain: Basic bodily sensation that is induced by a noxious stimulus, is received by naked
nerve endings, is characterized by physical discomfort (as pricking, throbbing, or
aching), and typically leads to evasive action.
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Pancreas: A gland with dual functions: The nonendocrine portion secretes digestive
enzymes and an alkaline solution into the small intestine via a duct; the endocrine
portion secretes the hormones insulin and glucagon into the blood.
Parathyroid Hormone: A hormone of the parathyroid gland that regulates the
metabolism of calcium and phosphorus in the body.
Pathogen: A specific causative agent (as a bacterium or virus) of disease.
Pedigree: A diagram of a family tree showing the heritable characters in parents and
offspring over multiple generations .
Pelvis: A basin-shaped structure in the skeleton of many vertebrates that is formed by
the pelvic girdle together with the sacrum and often various coccygeal and caudal
vertebrae and that in humans is composed of the two hip bones bounding it on each
side and in front while the sacrum and coccyx complete it behind.
Perimysium: The connective-tissue sheath that surrounds a muscle and forms sheaths
for the bundles of muscle fibers.
Peripheral Nervous System: The part of the nervous system that is outside the central
nervous system and comprises the cranial nerves excepting the optic nerve, the spinal
nerves, and the autonomic nervous system.
Peripheral Vascular Disease: Vascular disease (as Raynaud's disease and Buerger's
disease) affecting blood vessels outside of the heart and especially those vessels
supplying the extremities.
Peristalsis: Successive muscular contractions along the wall of a hollow muscular
structure.
Pharynx: An area in the vertebrate throat where air and food passages cross.
Phrenology: The study of the conformation of the skull based on the belief that it is
indicative of mental faculties and character.
Physiology: Science that deals with the functions of an organism or its parts.
Pituitary Gland: An endocrine gland at the base of the hypothalamus; consists of a
posterior lobe, which stores and releases two hormones produced by the hypothalamus,
and an anterior lobe, which produces and secretes many hormones that regulate
diverse body functions.
Plantar Flexion: Bending the foot in the direction of the plantar surface (sole).
Platelet: A fragment of cytoplasm enclosed in a cell membrane and lacking a nucleus;
found in the circulating blood; plays a role in hemostasis.
Plexus: Network of interlacing blood vessels or nerves.
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Posterior: Situated at or toward the hind part of the body.
Proximal: Situated next to or near the point of attachment or origin or a central point.
Pulmonary Circulation: The passage of venous blood from the right atrium of the heart
through the right ventricle and pulmonary arteries to the lungs where it is oxygenated
and its return via the pulmonary veins to enter the left atrium and participate in the
systemic circulation.
Pulse: A regularly recurrent wave of distension in arteries that results from the progress
through an artery of blood injected into the arterial system at each contraction of the
ventricles of the heart.
Pupil: The opening in the iris, which admits light into the interior of the vertebrate eye;
muscles in the iris regulate its size.
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R
Range of Motion: The range through which a joint can be moved.
Reaction Time: The time elapsing between the beginning of the application of a
stimulus and the beginning of an organism's reaction to it.
Reflex: An automatic and often inborn response to a stimulus that involves a nerve
impulse passing inward from a receptor to the spinal cord and thence outward to an
effector (as a muscle or gland) without reaching the level of consciousness and often
without passing to the brain.
Refraction: The deflection from a straight path undergone by a light ray or a wave of
energy in passing obliquely from one medium (as air) into another (as water or glass) in
which its velocity is different.
Regional Terms: Anatomical terms that refer to specific visible landmarks on the
surface of the body.
Residual Volume: The volume of air remaining in lungs after maximum exhalation.
Resource: A natural feature or phenomenon that enhances the quality of human life.
Restriction Enzyme: A degradative enzyme that recognizes specific nucleotide
sequences and cuts up DNA.
Restriction Fragment Length Polymorphisms (RFLPs): Differences in DNA
sequence on homologous chromosomes that can result in different patterns of
restriction fragment lengths (DNA segments resulting from treatment with restriction
enzymes).
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Resume: A brief written account of personal, educational, and professional
qualifications and experience, as that prepared by an applicant for a job.
Retina: The sensory membrane that lines most of the large posterior chamber of the
vertebrate eye, is composed of several layers including one containing the rods and
cones, and functions as the immediate instrument of vision by receiving the image
formed by the lens and converting it into chemical and nervous signals which reach the
brain by way of the optic nerve.
Rigor Mortis: Temporary rigidity of muscles occurring after death.
Rod: Any of the long rod-shaped photosensitive receptors in the retina responsive to
faint light.
Rotation: Moving a bone around its own axis, with no other movement.
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S
Salivary Amylase: A salivary gland enzyme that hydrolyzes starch.
Salivary Glands: Exocrine glands associated with the oral cavity. The secretions of
salivary glands contain substances to lubricate food, adhere together chewed pieces
into a bolus, and begin the process of chemical digestion.
Sarcomere: Any of the repeating structural units of striated muscle fibrils.
Sebaceous Gland: Any of the small sacculated glands lodged in the substance of the
derma, usually opening into the hair follicles, and secreting an oily or greasy material
composed in great part of fat which softens and lubricates the hair and skin.
Second-degree Burn: A burn marked by pain, blistering, and superficial destruction of
dermis with edema and hyperemia of the tissues beneath the burn.
Skeletal Muscle: An organ specialized for contraction, composed of striated muscle
fibers (cells), supported by connective tissue, attached to bone by a tendon or
aponeurosis, and stimulated by somatic motor neurons.
Skull: The skeleton of the head forming a bony case that encloses and protects the
brain and chief sense organs and supports the jaws.
Sliding Filament Mechanism: The explanation of how thick and thin filaments slide
relative to one another during striated muscle contraction to decrease sarcomere length.
Small Intestine: The part of the intestine that lies between the stomach and colon,
consists of duodenum, jejunum, and ileum, secretes digestive enzymes, and is the chief
site of the absorption of digested nutrients.
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Smooth Muscle: A tissue specialized for contraction, composed of smooth muscle
fibers (cells), located in the walls of hollow internal organs, and innervated by the
autonomic motor neurons.
Spirometer: An instrument for measuring the air entering and leaving the lungs.
Spongy Bone: Bone tissue that consists of an irregular latticework of thin plates of
bone called trabeculae; found inside short, flat, and irregular bones and in the
epiphyses of long bone.
Stomach: A saclike expansion of the alimentary canal of a vertebrate communicating
anteriorly with the esophagus and posteriorly with the duodenum and being typically a
simple often curved sac with an outer serous coat, a strong complex muscular wall that
contracts rhythmically, and a mucous lining membrane that contains gastric glands.
Striation: Any of the alternate dark and light cross bands of a myofibril of striated
muscle.
Stroke Volume: The volume of blood pumped from a ventricle of the heart in one beat.
Sulcus: A shallow furrow on the surface of the brain separating adjacent gyri.
Superficial: Of, relating to, or located near the surface.
Superior: Situated toward the head and further away from the feet than another and
especially another similar part of an upright body especially of a human being.
Suture: An immovable fibrous joint that joins skull bones.
Synapse: The place at which a nervous impulse passes from one neuron to another.
Synovial Cavity: The space between the articulating bones of a synovial joint, filled
with synovial fluid. Also called a joint cavity.
Synovial Fluid: Secretion of synovial membranes that lubricates joints and nourishes
articular cartilage.
Synovial Joint: A fully moveable joint in which the synovial (joint) cavity is present
between the two articulating bones.
System: A group of body organs or structures that together perform one or more vital
functions.
Systemic Circulation: The passage of arterial blood from the left atrium of the heart
through the left ventricle, the systemic arteries, and the capillaries to the organs and
tissues that receive much of its oxygen in exchange for carbon dioxide and the return of
the carbon-dioxide carrying blood via the systemic veins to enter the right atrium of the
heart and to participate in the pulmonary circulation.
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T
Tendon: A white fibrous cord of dense regular connective tissue that attaches muscle to
bone.
Third-degree Burn: Severe burn characterized by destruction of the skin through the
depth of the dermis and possibly into underlying tissues, loss of fluid, and sometimes
shock.
Thoracic Cavity: The body cavity in mammals that houses the lungs and heart. It is
surrounded in part by ribs and separated from the lower abdominal cavity by the
diaphragm.
Tibia: The inner and usually larger of the two bones of the leg between the knee and
ankle that articulates above with the femur and below with the talus -- called also
shinbone.
Tidal Volume: The volume of air breathed in and out without conscious effort.
Tissue: An integrated group of cells with a common structure and function.
T Lymphocyte (T cell): A type of lymphocyte responsible for cell-mediated immunity
that differentiates under the influence of the thymus.
Tropomyosin: A protein of muscle that forms a complex with troponin regulating the
interaction of actin and myosin in muscular contraction.
Troponin: A protein of muscle that together with tropomyosin forms a regulatory protein
complex controlling the interaction of actin and myosin and that when combined with
calcium ions permits muscular contraction.
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U
Ureter: A duct leading from the kidney to the urinary bladder.
Urethra: A tube that releases urine from the body near the vagina in females or through
the penis in males; also serves in males as the exit tube for the reproductive system.
Urinalysis: Chemical analysis of urine.
Urinary Bladder: The pouch where urine is stored prior to elimination.
Urinary System: The organs of the urinary tract comprising the kidneys, ureters,
urinary bladder, and urethra.
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Urine: Waste material that is secreted by the kidney, is rich in end products (as urea,
uric acid, and creatinine) of protein metabolism together with salts and pigments, and
forms a clear amber and usually slightly acid fluid.
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V
Valve: A bodily structure (as the mitral valve) that closes temporarily a passage or
orifice or permits movement of fluid in one direction only.
Varicose Vein: An abnormal swelling of a superficial vein of the legs.
Vein: Any of the tubular branching vessels that carry blood from the capillaries toward
the heart and have thinner walls than the arteries and often valves at intervals to
prevent reflux of the blood which flows in a steady stream and is in most cases darkcolored due to the presence of reduced hemoglobin.
Ventral: Being or located near, on, or toward the lower surface of an animal (as a
quadruped) opposite the back or dorsal surface; being or located near, on, or toward the
front or anterior part of the human body.
Ventricle: A chamber of the heart which receives blood from a corresponding atrium
and from which blood is forced into the arteries.
Venule: Any of the minute veins connecting the capillaries with the larger systemic
veins.
Vital Capacity: The total volume of air that can be exhaled after maximal inhalation.
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Human Body Systems Glossary – Page 19