Glossary
G-3
Atomic number
Te number of protons in an atom.
Atomic symbol
Te one- or two-letter symbol used to indicate an ele-
ment; usually the first letter(s) of the element’s name.
Atomic weight
Te average of the mass numbers of all the isotopes of an
element.
ATP (adenosine triphosphate)
(ah-den
9
o-sēn tri
0
fos
9
fāt) Organic mol-
ecule that stores and releases chemical energy for use in body cells.
Atria
(a
9
tre-ah) Te two superior receiving chambers of the heart.
Atrial natriuretic peptide (ANP)
(a
9
tre-al na
0
tre-u-ret
9
ik) A hormone
released by certain cells of the heart atria that reduces blood pressure and
blood volume by inhibiting nearly all events that promote vasoconstric-
tion and Na
1
and water retention.
Atrioventricular (AV) bundle
(a
0
tre-o-ven-trĭ
9
kyoo-ler) Bundle of spe-
cialized fibers that conduct impulses from the AV node to the right and
leF ventricles; also called bundle of His.
Atrioventricular (AV) node
Specialized mass of conducting cells lo-
cated at the atrioventricular junction in the heart.
Atrioventricular (AV) valve
Valve that prevents backflow into the
atrium when the connected ventricle is contracting.
Atrophy
(at
9
ro-fe) Reduction in size or wasting away of an organ or cell
resulting from disease or lack of use.
Auditory ossicles
(ah
9
sih-kulz) Te three tiny bones serving as transmit-
ters of vibrations and located within the middle ear: the malleus, incus,
and stapes.
Auditory tube
See
Pharyngotympanic tube.
Autoimmunity
Production of antibodies or effector ± cells that attack a
person’s own tissue.
Autolysis
(aw
0
tol
9
ĭ-sis) Process of autodigestion (self-digestion) of cells,
especially dead or degenerate cells.
Autonomic ganglion
Collection of sympathetic or parasympathetic
postganglionic neuronal cell bodies.
Autonomic nervous system (ANS)
Efferent division of the peripheral
nervous system that innervates cardiac and smooth muscles and glands;
also called the involuntary or visceral motor system.
Autonomic (visceral) reflexes
Reflexes that activate smooth or cardiac
muscle and/or glands.
Autoregulation
Te automatic local adjustment of blood flow to a par-
ticular body area in response to its current requirements.
Autosomes
Chromosomes number 1 to 22; do not include the sex
chromosomes.
Avogadro’s number
(av
0
o-gad
9
rōz) Te number of molecules in one
mole of any substance, 6.02
3
10
23
.
Axial
Relating to the head, neck, and trunk; one of the two major divi-
sions of the body.
Axolemma
(ak
0
so-lem
9
ah) Te plasma membrane of an axon.
Axon
Neuron process that carries impulses away from the nerve cell
body; efferent process; the conducting portion of a nerve cell.
Axon terminals (terminal boutons)
Te bulbous distal endings of the
terminal branches of an axon.
B cells
Also called B lymphocytes; oversee humoral immunity; their de-
scendants differentiate into antibody-producing plasma cells.
Baroreceptor
(bayr
0
o-re-sep
9
tor) A sensory nerve ending in the wall of
the carotid sinus or aortic arch sensitive to vessel stretching.
Basal body
(ba
9
sal) An organelle structurally identical to a centriole and
forming the base of a cilium or flagellum.
Basal ganglia
See
Basal nuclei.
Apnea
Breathing cessation.
Apocrine sweat gland
(ap
9
o-krin) Te less numerous type of sweat gland;
produces a secretion containing water, salts, proteins, and fatty acids.
Apoenzyme
(ap
9
ō-en-zīm) Te protein portion of an enzyme.
Aponeurosis
(ap
0
o-nu-ro
9
sis) ²ibrous or membranous sheet connecting
a muscle and the part it moves.
Apoptosis
A process of controlled cellular suicide; eliminates cells that
are unneeded, stressed, or aged.
Appendicitis
(ă-pen
9
dĭ-sī-
9
tis) Inflammation of the appendix (wormlike
sac attached to the cecum of the large intestine).
Appendicular
Relating to the limbs; one of the two major divisions of
the body.
Appositional growth
Growth accomplished by the addition of new lay-
ers onto those previously formed.
Aquaporins
0
kwă-por
9
ins) ±ransmembrane proteins that form water
channels.
Aqueous humor
(a
9
kwe-us) Watery fluid in the anterior segment of the eye.
Arachnoid
(ah-rak
9
noid) Weblike; specifically, the weblike arachnoid
mater, the middle layer of the three meninges.
Areola
(ah-re
9
o-lah) Circular, pigmented area surrounding the nipple;
any small space in a tissue.
Areolar connective tissue
A type of loose connective tissue.
Arrector pili
(ah-rek
9
tor pi
9
li) ±iny, smooth muscles attached to hair
follicles; contraction causes the hair to stand upright.
Arrhythmia
(a-rith
9
me-ah) Irregular heart rhythm, oFen caused by de-
fects in the intrinsic conduction system.
Arteries
Blood vessels that conduct blood away from the heart and into
the circulation.
Arteriole
(ar-tēr
9
e-ōl) A minute artery.
Arteriosclerosis
(ar-tē-r
9
e-o-skler-o
9
sis) Any of a number of prolifera-
tive and degenerative changes in the arteries leading to their decreased
elasticity.
Arthritis
Inflammation of the joints.
Arthroscopic surgery
(ar-thro-skop
9
ik) Procedure enabling a surgeon
to repair the interior of a joint through a small incision.
Articular capsule
Double-layered capsule composed of an outer fibrous
layer lined by synovial membrane; encloses the joint cavity of a synovial
joint.
Articular cartilage
Hyaline cartilage covering bone ends at movable
joints.
Articulation (joint)
Te junction of two or more bones.
Association areas
²unctional areas of the cerebral cortex that act mainly
to integrate diverse information for purposeful action.
Astigmatism
(ah-stig
9
mah-tizm) A condition in which unequal curvatures
in different parts of the cornea or lens of the eye lead to blurred vision.
Astrocyte
(as
9
tro-sīt) A type of CNS supporting cell; assists in exchanges
between blood capillaries and neurons.
Atelectasis
(at
0
ĕ-lik
9
tah-sis) Lung collapse.
Atherosclerosis
(a
0
ther-o
0
skler-o
9
sis) Changes in the walls of large
arteries consisting of lipid deposits on the artery walls; one form of
arteriosclerosis.
Atmospheric pressure
²orce that air exerts on the surface of the body
(760 mm Hg at sea level).
Atom
Smallest particle of an elemental substance that exhibits the prop-
erties of that element; composed of protons, neutrons, and electrons.
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