Bma Illustrated Medical Dictionary

man continues to achieve orgasm and
ejaculate as normal, but the semenno
longer contains sperm, which are reab-
sorbed in thetestes. Male sterilization
is a safe and effective method of contra-
ception. However, rarely, the severed
ends of a vas deferens reunite, and
sperm appear in the ejaculate. If this
occurs, the man can safely undergo
another vasectomy. Some operations to
restore fertility after vasectomy are suc-
cessful, but the process should be
regarded as irreversible.
vasoconstrictionNarrowing of blood
vessels, causing reduced blood flow to a
part of the body. Vasoconstriction under
the skin occurs in response to the cold
and reduces heat loss from the body.
vasodilationWidening of blood ves-
sels, causing increased blood flow to a
part of the body. Vasodilation under the
skin occurs in response to hot weather
and increases heat loss from the body.
vasodilator drugsA group of drugs
that widen blood vessels. Vasodilator
drugs include ACE inhibitors, alpha-
blockers, calcium channel blockers, nitrate
drugs, and sympatholytic drugs. They
are used to treat disorders in which
abnormal narrowing of blood vessels
reduces blood flow through tissues,
impairing the supply of oxygen. Such
disorders include angina pectorisand
peripheral vascular disease. Vasodilators
are also used to treat hypertensionand
heart failure. All vasodilator drugs may
cause flushing, headaches, dizziness,
fainting, and swollen ankles.
vasopressinAnother name for ADH.

vasovagal attackTemporary loss of

consciousness due to sudden slowing

of the heartbeat, usually brought on by

severe pain, stress, shock, or fear. A

vasovagal attack, a common cause of

faintingin healthy people, results from

overstimulation of the vagus nerve.

VDThe abbreviation for venereal dis-

ease, an outdated term for sexually

transmitted infections.

vectorAn animal that transmits a par-

ticular infectious disease. A vector picks

up disease-causing organisms from a

source of infection (such as an infected

person’s or animal’s blood or faeces),

carries them in or on its body, and later

deposits them where they infect a new

host, directly or indirectly. Mosquitoes,

fleas, lice, ticks, and flies are the most

important vectors of disease to humans.

veganismThe adoption of a diet that

excludes all meat and fish and all ani-

mal products, including milk and eggs.

A vegan diet is likely to result in vitamin

B 12 deficiency. Supplements are essen-

tial during pregnancy.

vegetarianismEating a diet that ex-

cludes meat and fish, and sometimes

all other animal products. Humans do

not need to eat meat or animal prod-

ucts to maintain health as long as the

nutrients supplied by plant foods pro-

vide a balanced diet (see nutrition).

However, people who exclude all animal

products (vegans) need to plan their

diet carefully or take supplements to

avoid vitamin B 12 or calciumdeficiency.

Vegetarian diets are relatively rich in

fibre, which may help protect against

VASECTOMY

VASOCONSTRICTION VEGETARIANISM

V

Bladder

SITES OF

INCISIONS

Vas

deferens

Area to be

removed

Penis

Testis

Bladder

Penis

Testis

BEFORE THE PROCEDURE AFTER THE PROCEDURE

Vas

deferens

Secured

ends