Glossary
G-23
Vasomotor fibers
Sympathetic nerve fibers that cause the contraction
of smooth muscle in the walls of blood vessels, thereby regulating blood
vessel diameter.
Veins
(vānz
0
) Blood vessels that return blood toward the heart from the
circulation.
Ventral
Pertaining to the front; anterior.
Ventricles
(1) Paired, inferiorly located heart chambers that function as
the major blood pumps; (2) cavities in the brain.
Venule
(ven
9
ūl) A small vein.
Vertebral column (spine)
(ver
9
tĕ-brul) Formed of a number of indi-
vidual bones called vertebrae and two composite bones (sacrum and
coccyx).
Vesicle
(vĕ
9
sĭ-kul) A small liquid-filled sac or bladder.
Vesicular transport
Transport of large particles and macromolecules into
or out of a cell or between its compartments in membrane-bound sacs.
Vesicular follicle
Mature ovarian follicle.
Vestibule
An enlarged area at the beginning of a canal, i.e., inner ear,
nose, larynx.
Villus
(vil
9
us) One of the fingerlike projections of the small intestinal
mucosa that tremendously increase its surface area for absorption.
Visceral
(vis
9
er-al) Pertaining to an internal organ of the body or the in-
ner part of a structure.
Visceral muscle
Type of smooth muscle; its cells contract as a unit and
rhythmically, are electrically coupled by gap junctions, and o±en exhibit
spontaneous action potentials. Also called unitary smooth muscle.
Visceral organs (viscera)
A group of internal organs housed in the ven-
tral body cavity.
Visceral serosa
(se-ro
9
sah) ²e part of the double-layered membrane
that lines the outer surfaces of organs within the ventral body cavity.
Viscosity
(vis
9
kos
9
ĭ-te) A measurement of thickness (stickiness) of a fluid.
Visual field
²e field of view seen when the head is still.
Vital capacity (VC)
²e volume of air that can be expelled from the
lungs by forcible expiration a±er the deepest inspiration; total exchange-
able air.
Vital signs
Includes pulse, blood pressure, respiratory rate, and body
temperature measurements.
Vitamins
Organic compounds required by the body in minute amounts.
Vocal folds
Mucosal folds that function in voice production (speech);
also called the true vocal cords.
Volatile acid
An acid that can be eliminated by the lungs; carbonic acid
is converted to CO
2
, which diffuses into the alveoli.
Volkmann’s canals
See
Perforating canals.
Voluntary muscle
Muscle under strict nervous control; skeletal muscle.
Voluntary nervous system
²e somatic nervous system.
Vulva
(vul
9
vuh) Female external genitalia.
Wallerian degeneration
(wal-er
9
ē-an) A process of disintegration of an
axon that occurs when it is crushed or severed and cannot receive nutri-
ents from the cell body.
White matter
White substance of the central nervous system; myelin-
ated nerve fibers.
XenograF
Tissue gra± taken from another animal species.
Yolk sac
(yōk) One of the extraembryonic membranes; involved in early
blood cell formation.
Zygote
(zi
9
gōt) Fertilized egg.
Trypsin
Proteolytic enzyme secreted by the pancreas.
Tubular reabsorption
²e movement of filtrate components from the
renal tubules into the blood.
Tubular secretion
²e movement of substances (such as drugs, urea,
excess ions) from blood into filtrate.
Tumor
An abnormal growth of cells; a swelling; may be cancerous.
Tunica
(too
9
nĭ-kah) A covering or tissue coat; membrane layer.
Tympanic membrane
(tim-pan
9
ik) Eardrum.
Ulcer
(ul
9
ser) Lesion or erosion of the mucous membrane, such as gas-
tric ulcer of stomach.
Umbilical cord
(um-bĭ
9
lĭ-kul) Structure bearing arteries and veins con-
necting the placenta and the fetus.
Umbilicus
(um-bĭ
9
lĭ-kus) Navel; marks site where umbilical cord was
attached in fetal stage.
Unipolar neuron
Neuron in which embryological fusion of the two pro-
cesses leaves only one process extending from the cell body.
Uracil (U)
(u
9
rah-sil) A smaller, single-ring base (a pyrimidine) found
in RNA.
Urea
(u-re
9
ah) Main nitrogen-containing waste excreted in urine.
Ureter
(u-re
9
ter) Tube that carries urine from kidney to bladder.
Urethra
(u-re
9
thrah) Canal through which urine passes from the bladder
to outside the body.
Uric acid
²e nitrogenous waste product of nucleic acid metabolism;
component of urine.
Urinary bladder
A smooth, collapsible, muscular sac that stores urine
temporarily.
Urinary system
System primarily responsible for water, electrolyte, and
acid-base balance and removal of nitrogenous wastes.
Uterine tube
(u
9
ter-in) Tube through which the ovum is transported to
the uterus. Also called fallopian tube.
Uterus
(u
9
ter-us) Hollow, thick-walled organ that receives, retains, and
nourishes fertilized egg; site where embryo/fetus develops.
Uvula
(u
9
vu-lah) Tissue tag hanging from so± palate.
Vaccine
Preparation that provides artificially acquired active immunity.
Vagina
²in-walled tube extending from the cervix to the body exterior;
o±en called the birth canal.
Valence shell
(va
9
lens) Outermost electron shell (energy level) of an
atom that contains electrons.
Varicosities
Knoblike swellings of certain autonomic axons containing
mitochondria and synaptic vesicles.
Vas
(vaz
9
) A duct; vessel.
Vasa recta
(va
9
sah rek
9
tah) Capillary branches that supply nephron
loops in the medulla region of the kidney.
Vascular
Pertaining to blood vessels or richly supplied with blood vessels.
Vascular spasm
Immediate response to blood vessel injury; results in
constriction.
Vasoconstriction
(vas
0
o-kon-strik
9
shun) Narrowing of blood vessels.
Vasodilation
(vas
0
o-di-la
9
shun) Relaxation of the smooth muscles of the
blood vessels, producing dilation.
Vasomotion
(vas
0
o-mo
9
shun) Intermittent contraction or relaxation of
the precapillary sphincters, resulting in a staggered blood flow when tis-
sue needs are not extreme.
Vasomotor center
(vas
0
o-mo
9
ter) Brain area concerned with regulation
of blood vessel resistance.
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