Glossary
719
anus
lowest opening of the digestive tract through
which fecal matter is extruded
aorta
(a-OR-tah) largest artery in body; carries
blood from left ventricle of heart to thorax and
abdomen
aortic arch baroreceptor
(a-OR-tik)
see
arterial
baroreceptor
aortic body chemoreceptor
chemoreceptor
located near aortic arch; sensitive to arterial
blood O
2
pressure and H
+
concentration
aortic valve
valve between left ventricle of heart
and aorta
apneustic center
area in the lower pons in the
brain with input to the medullary inspiratory
neurons; helps to terminate inspiration
apoptosis
(ay-pop-TOE-sis) programmed
cell death that typically occurs during
differentiation and development
appendix
small fi ngerlike projection from cecum
of large intestine
aquaporin
(ah-qua-PORE-in) protein membrane
channel through which water can diffuse
aqueous
(AY-kwee-us) watery; prepared with water
aqueous humor
fl uid fi lling the anterior chamber
of the eye
arachidonic acid
(ah-rak-ah-DON-ik)
polyunsaturated fatty acid precursor of
eicosanoids
arachnoid mater
(ah-RAK-noid) the middle of
three membranes (meninges) covering the
brain
area postrema
a circumventricular organ outside
the blood-brain barrier
aromatase
enzyme that converts androgens
to estrogens; located predominantly in the
ovaries, the placenta, the brain, and adipose
tissue
arrhythmia
(ay-RYTH-me-ah) any variation from
normal heartbeat rhythm
arterial baroreceptor
nerve endings sensitive to
stretch or distortion produced by arterial blood
pressure changes; located in carotid sinus or
aortic arch; also called carotid sinus and aortic
arch baroreceptors
arteriole
(are-TEER-ee-ole) blood vessel between
artery and capillary, surrounded by smooth
muscle; primary site of vascular resistance
arteriosclerosis
(are-TEER-ee-oh-sklare-OH-
sis) “hardening” of arterial walls that can
have different causes, including deposition of
collagenous fi bers that occurs with aging
artery
(ARE-ter-ee) thick-walled elastic vessel that
carries blood away from heart to arterioles
ascending limb
portion of Henle’s loop of renal
tubule leading to distal convoluted tubule
ascending pathway
neural pathway that goes to
the brain; also called sensory pathway
aspartate
(ah-SPAR-tate) an excitatory
neurotransmitter in CNS; ionized form of the
amino acid aspartic acid
aspiration
inhalation of liquid or a foreign body
into the airways
association cortex
see
cortical association area
astrocyte
a form of glial cell that regulates
composition of extracellular fl uid around
neurons and forms part of the blood-brain
barrier
atmospheric pressure (
P
atm
)
air pressure
surrounding the body (760 mmHg at sea level)
atom
smallest unit of matter that has unique
chemical characteristics; has no net charge;
combines with other atoms to form chemical
substances
atomic nucleus
dense region, consisting of
protons and neutrons, at center of atom
atomic number
number of protons in nucleus of
atom
atomic weight
value that indicates an atom’s mass
relative to mass of other types of atoms based on
the assignment of a value of 12 to carbon atom
ATP
see
adenosine triphosphate
ATPase
(aa-tea-PEE-ase) enzyme that breaks
down ATP to ADP and inorganic phosphate
atresia
degeneration of nondominant follicles in
the ovary
atrial natriuretic peptide (ANP)
(nay-tree-yor-
ET-ik) peptide hormone secreted by cardiac
atrial cells in response to atrial distension;
causes increased renal sodium excretion
atrioventricular (AV) node
(ay-tree-oh-ven-
TRIK-you-lar) region at base of right atrium
near interventricular septum, containing
specialized cardiac muscle cells through which
electrical activity must pass to go from atria to
ventricles
atrioventricular (AV) valve
valve between atrium
and ventricle of heart; AV valve on right side of
heart is the
tricuspid valve,
and that on left side
is the
mitral valve
atrium
(AY-tree-um) chamber of heart that
receives blood from veins and passes it on to
ventricle on same side of heart
atrophy
(AT-roh-fee) wasting away; decrease in
size
atropine
(AT-roh-peen) a drug that specifi cally
blocks the binding of acetylcholine to
muscarinic acetylcholine receptors
auditory
(AW-dih-tor-ee) pertaining to sense of
hearing
auditory cortex
region of cerebral cortex that
receives nerve fi bers from auditory pathways
autocrine agent
(AW-toh-crin) chemical
messenger secreted into extracellular fl uid
that acts upon cell that secreted it;
compare
paracrine agent
automaticity
(aw-toh-mah-TISS-ih-tee) capable
of spontaneous, rhythmical self-excitation
autonomic ganglion
group of neuron cell bodies
in the peripheral nervous system
autonomic nervous system
(aw-toh-NAHM-ik)
component of efferent division of peripheral
nervous system that consists of sympathetic
and parasympathetic subdivisions; innervates
cardiac muscle, smooth muscle, and glands;
compare
somatic nervous system
autoreceptor
a receptor on a cell affected by a
chemical messenger released from the same cell
autoregulation
(aw-toh-reg-you-LAY-shun)
ability of an individual organ to control (self-
regulate) its vascular resistance independent
of neural and hormonal infl uence;
see also
fl ow
autoregulation
autosome
chromosome that contains genes for
proteins governing most cell structures and
functions;
compare
sex chromosome
autotransfusion
shift of fl uid from the interstitial
space to the blood following a decrease in
blood pressure
axo-axonic synapse
presynaptic synapse where
an axon stimulates the presynaptic terminal
of another axon
axon
(AX-ahn) extension from neuron cell
body; propagates action potentials away from
cell body; also called a nerve fi ber
axon hillock
part of the axon nearest the cell
body where the action potential begins
axon terminal
end of axon; forms synaptic or
neuroeffector junction with postjunctional
cell
axonal transport
process involving intracellular
fi laments by which materials are moved from
one end of axon to other
B
B cell
(immune system) lymphocyte that, upon
activation, proliferates and differentiates into
antibody-secreting plasma cell; (endocrine
cell)
see
beta cell
B lymphocyte
see
B cell
barometric pressure
see
atmospheric pressure
baroreceptor
receptor sensitive to pressure and
to rate of change in pressure;
see also
arterial
baroreceptor, intrarenal baroreceptor
Barr body
sex chromatin nuclear mass formed
by the nonfunctional X chromosome in
female cell nuclei
basal
(BAY-sul) resting level
basal cell
cell found within taste buds that can
divide and differentiate to replace worn-out
taste receptor cells
basal metabolic rate (BMR)
metabolic rate
when a person is at mental and physical
rest but not sleeping, at comfortable
temperature, and has fasted at least 12 h; also
called metabolic cost of living
basal nuclei
nuclei deep in cerebral hemispheres
that code and relay information associated
with control of body movements; specifi cally,
caudate nucleus, globus pallidus, and
putamen; also called
basal ganglia
base
(acid-base) any molecule that can
combine with H
+
; (nucleotide) molecular
ring of carbon and nitrogen that, with a
phosphate group and a sugar, constitutes a
nucleotide
basement membrane
thin layer of extracellular
proteinaceous material upon which epithelial
and endothelial cells sit
basic electrical rhythm
spontaneous
depolarization-repolarization cycles of
pacemaker cells in longitudinal smooth
muscle layer of stomach and intestines;
coordinates repetitive muscular activity of
GI tract
basilar membrane
(BAS-ih-lar) membrane that
separates cochlear duct and scala tympani in
inner ear; supports organ of Corti
basolateral membrane
(bay-so-LAH-ter-al)
sides of epithelial cell other than luminal
surface; also called serosal or blood side
of cell
basophil
(BAY-so-fi ll) polymorphonuclear
granulocytic leukocyte whose granules stain
with basic dyes; enters tissues and becomes
mast cell
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