G-2 Glossaryapoptosis (ap 0 ̆o-to 9 sis) Cellular death in which
the cells show characteristic histological changes.
It occurs as part of programmed cell death and
other events in which cell death is a physiological
response.
aquaporins ( ̆a-kw ̆a-por 9 inz) The protein channels
in a cell (plasma) membrane that permit osmosis
to occur across the membrane. In certain tissues,
particularly the collecting ducts of the kidney,
aquaporins are inserted into the cell membrane in
response to stimulation by anti diuretic hormone.
aqueous humor (a 9 kwe-us) A fluid produced by
the ciliary body that fills the anterior and pos terior
chambers of the eye.
arginine vasopressin (ar’ji-nen va-so-pres’in)
The neuropeptide hormone produced by neurons
in the hypothalamus and stored in the posterior
pituitary (neurohypophysis). When it is secreted into
the blood, it acts on the kidneys to function as the
antidiuretic hormone (ADH).
arteriosclerosis (ar-tir 0 e-o-skl ̆e-ro 9 sis) Any of a
group of diseases characterized by thickening and
hardening of the artery wall and narrowing of its
lumen.
arteriovenous anastomosis (ar-tir 0 e-o-ve 9 nus
̆a-nas 0 t ̆o-mo 9 sis) A direct connection between an
artery and a vein that bypasses the capillary bed.
artery (ar 9 t ̆e-re) A vessel that carries blood away
from the heart.
astigmatism ( ̆a-stig 9 m ̆a-tiz 0 em) Unequal curvature
of the refractive surfaces of the eye (cornea and/or
lens), so that light that enters the eye along certain
meridians does not focus on the retina.
atherosclerosis (ath 0 ̆e-ro-skl ̆e-ro 9 sis) A common
type of arteriosclerosis in which raised areas, or
plaques, within the tunica interna of medium and
large arteries are formed from smooth muscle cells,
cholesterol, and other lipids. These plaques occlude
the arteries and serve as sites for the formation of
thrombi.
atomic number A whole number representing the
number of positively charged protons in the nucleus
of an atom.
atopic dermatitis ( ̆a-top 9 ik der 0 m ̆a-ti 9 tis) An
allergic skin reaction to agents such as poison ivy
and poison oak; a type of delayed hypersensitivity.
ATP adenosine triphosphate ( ̆aden 9 o ̆-s ̄en tri-
fos 9 f ̄at). The universal energy carrier of the cell.
atretic ( ̆a-tret 9 ik) Without an opening. Atretic
ovarian follicles are those that fail to rupture and
release an oocyte.
atrial natriuretic (a 9 tre-al na 0 tr ̆ı-yoo-ret 9 ik)
peptide (ANP) A chemical secreted by the atria
that acts as a natriuretic hormone (a hormone that
promotes the urinary excretion of sodium).
atrioventricular node (a 0 tre-o-ven-trik 9 y ̆u-lar
n ̄od) A specialized mass of conducting tissue
located in the right atrium near the junction of the
interventricular septum. It transmits the impulse into
the bundle of His; also called the AV node.
atrioventricular valves One-way valves located
between the atria and ventricles. The AV valve on
the right side of the heart is the tricuspid, and the AV
valve on the left side is the bicuspid, or mitral, valve.
atrophy (at 9 r ̆ofe) A gradual wasting away, or
decrease in mass and size of an organ; the opposite
of hypertrophy.
atropine (at 9 r ̆o-p ̄en) An alkaloid drug, obtained
from a plant of the species Belladonna, that acts
as an anticholinergic agent. It is used medically
to inhibit parasympathetic nerve effects, dilate the
pupil of the eye, increase the heart rate, and inhibit
intestinal movements.anemia ( ̆a-ne 9 me- ̆a) An abnormal reduction in
the red blood cell count, hemoglobin concentration,
or hematocrit, or any combination of these
measurements. This condition is associated with a
decreased ability of the blood to carry oxygen.
angina pectoris (an-ji 9 n ̆a pek 9 t ̆o-ris) A thoracic
pain, often referred to the left pectoral and arm area,
caused by myocardial ischemia.
angiogenesis (an 0 je-o-jen 9 e-sis) The growth of
new blood vessels.
angiotensin II (an 0 je-o-ten 9 sin) An eight-
amino-acid polypeptide formed from angiotensin I
(a ten-amino-acid precursor), which in turn is formed
from the cleavage of a protein (angio tensinogen)
by the action of renin, an enzyme secreted by the
kidneys. Angiotensin II is a powerful vasoconstrictor
and a stimulator of aldosterone secretion from the
adrenal cortex.
anion (an 9 i-on) An ion that is negatively charged,
such as chloride, bicarbonate, or phosphate.
antagonistic effects Actions of regulators such as
hormones or nerves that counteract the effects
of other regulators. The actions of sympathetic and
parasympathetic neurons on the heart, for example,
are antagonistic.
anterior pituitary (p ̆ı-too 9 ı ̆-ter-e ) See
adenohypophysis.
antibodies (an 9 t ̆ı-bod 0 ̄ez) Immunoglobulin
proteins secreted by B lymphocytes that have
been transformed into plasma cells. Antibodies are
responsible for humoral immunity. Their synthesis
is induced by specific antigens, and they combine
with these specific antigens but not with unrelated
antigens.
anticoagulant (an 0 te-ko-ag 9 y ̆u-lant) A substance
that inhibits blood clotting.
anticodon (an 0 te-ko 9 don) A base triplet provided
by three nucleotides within a loop of transfer RNA
that is complementary in its base-pairing properties
to a triplet (the codon in mRNA). The matching
of codon to anticodon provides the mechanism
for translation of the genetic code into a specific
sequence of amino acids.
antigen (an 9 t ̆ı-jen) A molecule able to induce the
production of antibodies and to react in a specific
manner with antibodies.
antigenic (an-t ̆ı-jen 9 ik) determinant site The
region of an antigen molecule that specifically reacts
with particular antibodies. A large antigen molecule
may have a number of such sites.
antioxidants Molecules that scavenge free
radicals, thereby relieving the oxidative stress on the
body.
antiport (an 9 -t ̆ı-port) A form of secondary active
transport (coupled transport) in which a molecule
or ion is moved together with, but in the opposite
direction to, Na^1 ions; that is, out of the cell; also
called countertransport.
antiserum (an 9 t ̆ı-se 0 rum) A serum containing
antibodies that are specific for one or more antigens.
aphasia ( ̆a-fa 9 ze- ̆a) Absent or defective speech,
writing, or comprehension of written or spoken
language caused by brain damage or disease. Broca’s
area, Wernicke’s area, the arcuate fasciculus, or the
angular gyrus may be involved.
apnea (ap 9 ne- ̆a) The temporary cessation of
breathing.
apneustic (ap-noo 9 stik) center A collection of
neurons in the brain stem that participates in the
rhythmic control of breathing.
apolipoprotein (ap 9 o-lip-o-pro 9 ten) The
protein component of plasma lipoproteins, such as
chylomicrons, LDL, and HDL.allergen (al 9 -er-jen) An antigen that evokes an
allergic response rather than a normal immune
response.
allergy (al 9 er-je) A state of hypersensitivity caused
by exposure to allergens. It results in the liberation
of histamine and other molecules with histamine-like
effects.
all-or-none law The statement that a given
response will be produced to its maximum extent
in response to any stimulus equal to or greater than
a threshold value. Action potentials obey an all-or-
none law.
allosteric (al 0 o-ster 9 ik) Denoting the alteration
of an enzyme’s activity by its combination with a
regulator molecule. Allosteric inhibition by an end
product represents negative feedback control of an
enzyme’s activity.
alpha motoneuron (al 9 f ̆a mo 0 t ̆o-noor 9 on) The type
of somatic motor neuron that stimulates extrafusal
skeletal muscle fibers.
alveoli (al-ve 9 ̆o-li); sing., alveolus. Small, saclike
dilations (as in lung alveoli).
amniocentesis (am 0 ne-o-sen-te 9 sis) A procedure
for obtaining amniotic fluid and fetal cells in this
fluid through transabdominal perforation of the
uterus.
amnion (am 9 ne-on) A developmental membrane
surrounding the fetus that contains amniotic fluid;
commonly called the “bag of waters.”
amoeboid (ah-me 9 boid) movement Movement of
a cell from place to place using pseudopods, the way
an amoeba (a single-celled animal) moves.
amphoteric (am-fo-ter 9 ik) Having both acidic and
basic characteristics; used to denote a molecule that
can be positively or negatively charged, depending
on the pH of its environment.
amylase (am 9 il- ̄as) A digestive enzyme that
hydrolyzes the bonds between glucose subunits in
starch and glycogen. Salivary amylase is found in saliva
and pancreatic amylase is found in pancreatic juice.
an- (Gk.) Without; not.
anabolic steroids (an 0 ̆a-bol 9 ik ster 9 oidz) Steroids
with androgen-like stimulatory effects on protein
synthesis.
anabolism ( ̆a-nab 9 ̆o-liz 0 em) Chemical reactions
within cells that result in the production of larger
molecules from smaller ones; specifically, the
synthesis of protein, glycogen, and fat.
anaerobic (an-a-ro 9 bik) metabolism The
metabolic pathway that provides energy for cells in
the absence of oxygen. In animal cells, this refers to
lactic acid fermentation, the formation of lactic acid
from glucose. In the process, two ATP are formed
per glucose molecule.
anaerobic threshold The maximum rate of oxygen
consumption that can be attained before a significant
amount of lactic acid is produced by the exercising
skeletal muscles through anaerobic respiration. This
generally occurs when about 60% of the person’s
total maximal oxygen uptake has been reached.
anaphylaxis (an 0 ̆a-f ı ̆-lak 9 sis) An unusually severe
allergic reaction that can result in cardiovascular
shock and death.
androgen (an 9 dr ̆o-jen) A steroid hormone that
controls the development and maintenance of
masculine characteristics; primarily testosterone
secreted by the testes, although weaker androgens are
secreted by the adrenal cortex.
androgen-binding protein (ABP) A protein
produced by the Sertoli cells and released into the
lumen of the seminiferous tubules. It is believed
to concentrate testosterone in the lumen of these
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