Glossary G-19the body. Vitamins are classified as water-soluble or
fat-soluble.
voltage-regulated channel A protein in the
plasma membrane that can open to produce an
aqueous channel for the passage of ions through
the membrane. The channel opens in response the
stimulus of a depolarization to a threshold level. Also
called a voltage-gated channel.W
white matter The portion of the central nervous
system composed primarily of myelinated fiber
tracts. This forms the region deep to the cerebral
cortex in the brain and the outer portion of the spinal
cord.Z
zygote (zi 9 g ̄ot) A fertilized ovum.
zymogen (zi 9 m ̆o-jen) An inactive enzyme that
becomes active when part of its structure is removed
by another enzyme or by some other means.vasopressin (va 0 zo-pres 9 in) Another name for
antidiuretic hormone (ADH), released from the
posterior pituitary. The name vasopressin is derived
from the fact that this hormone can stimulate
constriction of blood vessels.
vein A blood vessel that returns blood to the heart.
ventilation (ven 0 t ̆ı-la 9 shun) Breathing; the process
of moving air into and out of the lungs.
vertigo (ver 9 t ̆ı-go) A sensation of whirling motion,
either of oneself or of external objects; dizziness, or
loss of equilibrium.
vestibular (v ̆e-stib 9 y ̆u-lar) apparatus The parts
of the inner ear, including the semicircular canals,
utricle, and saccule, that function to provide a sense
of equilibrium.
villi (vil 9 i) Fingerlike folds of the mucosa of the
small intestine.
virulent (vir 9 y ̆u-lent) Pathogenic, or able to cause
disease.
vital capacity The maximum amount of air that
can be forcibly expired after a maximal inspiration.
vitamin (vi 9 t ̆a-min) Any of various unrelated
organic molecules present in foods that are required
in small amounts for normal metabolic function ofvagina (v ̆a-ji 9 n ̆a) The tubular organ in the female
leading from the external opening of the vulva to the
cervix of the uterus.
vagus (va 9 gus) nerve The tenth cranial nerve,
composed of sensory dendrites from visceral organs
and preganglionic parasympathetic nerve fibers. The
vagus is the major parasympathetic nerve in the body.
Valsalva (val-sal 9 vaz) maneuver Exhalation
against a closed glottis, so that intrathoracic pressure
rises to the point that the veins returning blood to
the heart are partially constricted. This produces
circulatory and blood pressure changes that could be
dangerous.
vasa vasora (va 9 s ̆a va-sor 9 ̆a) Blood vessels that
supply blood to the walls of large blood vessels.
vasectomy (v ̆a-sek 9 t ̆o-me, va-zek 9 t ̆o-me) Surgical
removal of a portion of the ductus (vas) deferens to
induce infertility.
vasoconstriction (va 0 zo-kon-strik 9 shun) A
narrowing of the lumen of blood vessels as a result of
contraction of the smooth muscles in their walls.
vasodilation (va 0 zo-di-la 9 shun) A widening of the
lumen of blood vessels as a result of relaxation of the
smooth muscles in their walls.fox36375_glo_G1-G19.indd 19fox36375_glo_G1-G19.indd 19 2/4/15 12:29 PM2/4/15 12:29 PM