Vascular spasm Contraction of the smooth muscle in the wall of a
damaged blood vessel to prevent blood loss.
Vascular (venous) sinus A vein with a thin endothelial wall that lacks
a tunica media and externa and is supported by surrounding
Vascular tunic (TOO-nik) The middle layer of the eyeball, composed
of the choroid, ciliary body, and iris. Also called the uvea (0-ve-a).
Vasectomy (va-SEK-to-me) A means of sterilization of males in which
a portion of each ductus (vas) deferens is removed.
Vasoconstriction (vaz-o-kon-STRIK-shun) A decrease in the size of
the lumen of a blood vessel caused by contraction of the smooth
muscle in the wall of the vessel.
Vasodilation (vaz'-o-DT-la-shun) An increase in the size of the lumen
of a blood vessel caused by relaxation of the smooth muscle in
the wall of the vessel.
Vein (VAN) A blood vessel that conveys blood from tissues back to
Vena cava (VE-na KA-va) One of two large veins that open into the
right atrium, returning to the heart all of the deoxygenated blood
from the systemic circulation except from the coronary circulation.
Ventral (VEN-tral) Pertaining to the anterior or front side of the body;
opposite of dorsal.
Ventricle (VEN-tri-kul) A cavity in the brain filled with cerebrospinal
fluid. An inferior chamber of the heart.
Ventricular fibrillation (ven-TRIK-u-lar fib-ri-LA-shun) Asynchronous
ventricular contractions; unless reversed by defibrillation, results
in heart failure.
Venule (VEN-ul) A small vein that collects blood from capillaries and
delivers it to a vein.
Vermiform appendix (VER-mi-form a-PEN-diks) A twisted, coiled tube
attached to the cecum.
Vertebral cavity (VER-te-bral) A space within the vertebral column
formed by the vertebral foramina of all the vertebrae and contain-
ing the spinal cord.
Vertebral column The 26 vertebrae of an adult and 33 vertebrae of
a child; encloses and protects the spinal cord and serves as a
point of attachment for the ribs and back muscles. Also called the
backbone, spine, or spinal column.
Vesicle (VES-i-kul) A small bladder or sac containing liquid.
Vestibular apparatus (ves-TIB-u-lar) Collective term for the organs of
equilibrium, which includes the saccule, utricle, and semicircular
Vestibular membrane The membrane that separates the cochlear
duct from the scala vestibuli.
Vestibule (VES-ti-bul) A small space or cavity at the beginning of a
canal, especially the inner ear, larynx, mouth, nose, and vagina.
Villus (VIL-lus) A projection of the intestinal mucosal cells containing
connective tissue, blood vessels, and a lymphatic vessel; func-
tions in the absorption of the end products of digestion.
P lu r a l
Viscera (VIS-er-a) The organs inside the thoracic and abdominopelvic
S in g u la r
is viscus (VIS-kus).
Visceral (VIS-er-al) Pertaining to the organs or to the covering of an
Visceral effectors (e-FEK-torz) Organs of the thoracic and abdomi-
nopelvic cavities that respond to neural stimulation, including
cardiac muscle, smooth muscle, and glands.
Vital capacity The sum of inspiratory reserve volume, tidal volume,
and expiratory reserve volume; about 4800 mL in males.
Vital signs Signs necessary to life that include temperature (T), pulse
(P), respiratory rate (RR), and blood pressure (BP).
Vitamin An organic molecule necessary in trace amounts that acts
as a catalyst in normal metabolic processes in the body.
Vitreous body (VIT-re-us) A soft, jellylike substance that fills the
vitreous chamber of the eyeball, lying between the lens and the
Vocal folds Pair of mucous membrane folds below the ventricular
folds that function in voice production. Also called true vocal
Voltage-gated channel An ion channel in a plasma membrane com-
posed of integral proteins that functions like a gate to permit or
restrict the movement of ions across the membrane in response
to changes in the voltage.
Vulva (VUL-va) Collective designation for the external genitals of the
female. Also called the pudendum (poo-DEN-dum).
Wallerian degeneration (wal-LE-re-an) Degeneration of the portion of
the axon and myelin sheath of a neuron distal to the site of injury.
Wandering macrophage (MAK-ro-faj) Phagocytic cell that develops
from a monocyte, leaves the blood, and migrates to infected
Wave summation (sum-MA-shun) The increased strength of muscle
contraction that results when muscle action potentials occur one
after another in rapid succession.
White matter Aggregations or bundles of myelinated and unmyelin-
ated axons located in the brain and spinal cord.
Xiphoid (ZT-foyd) Sword-shaped. The inferior portion of the sternum
is the xiphoid process.
Yolk sac An extraembryonic membrane composed of the exocoe-
lomic membrane and hypoblast. It transfers nutrients to the
embryo, is a source of blood cells, contains primordial germ cells
that migrate into the gonads to form primitive germ cells, forms
part of the gut, and helps prevent desiccation of the embryo.
Zona pellucida (pe-LOO-si-da) Clear glycoprotein layer between a
secondary oocyte and the surrounding granulosa cells of the
Zygote (ZI-g-ot) The single cell resulting from the union of male and
female gametes; the fertilized ovum.