VINCA ALKALOIDS
VIRUSES
V
of
capillaries.
Its surface is covered with
hundreds of hairlike structures (micro-
villi). The villi and microvilli provide a
large surface area for absorption of food
molecules from the intestine into the
blood and the lymphatic system.
vinca alkaloids A group of substances
derived from the periwinkle plant (
VINCA
rosea)
that are used to treat
leukaemias,
lymphomas,
and some solid tumours,
such as
breast cancer
and
lung cancer.
All vinca alkaloids can cause neurological
toxicity, which appears as
neuropathy
.
Other side effects may include abdomi-
nal pain, constipation, and reversible
alopecia
. Common vinca alkaloids are
vinblastine, vindesine, and
vincristine.
Vincent's
disease A severe form of
gingivitis in which bacterial infection
causes painful ulceration of the gums.
(See also
gingivitis, acute ulcerative.)
vincristine A
vinca alkaloid
used to treat
certain cancers. One particular side effect
of vincristine is peripheral or autonomic
neuropathy
; but, unlike the other vinca
alkaloids, it causes very little reduction
in blood-cell production by the bone
marrow. Other side effects may include
abdominal pain, constipation, and re-
versible
alopecia
.
viraemia The presence of
virus
particles
in the blood. Viraemia can occur at cer-
tain stages in a variety of viral infections.
Some viruses, such as those responsi-
ble for viral
hepatitis
,
yellow fever
, and
poliomyelitis
, are transported in the
bloodstream. Others, such as the
rubella
virus and
HIV
, multiply in, and spread
via, certain white blood cells. If viraemia
is a feature of a viral infection, there is a
risk that the infection may be transmitted
to other people in blood or blood prod-
ucts, or by insects that feed on blood.
viral haemorrhagic fever Diseases
that are prevalent in Africa and cause
severe bleeding. There are several types,
including Ebola fever, Lassa fever, Han-
tavirus, and Marburg fever. The diseases
are fatal in a large percentage of cases,
but Lassa fever may respond to
antiviral
drugs
if given in the
1
st week.
virginity The physical state of not hav-
ing experienced sexual intercourse.
virilism The presence in a woman of
masculine characteristics. Virilism is
caused by excessive levels of
androgen
hormones
. Androgens are male sex hor-
mones which, in women, are normally
secreted in
small
amounts by the
adrenal glands and ovaries. Raised levels
induce various changes in women, in-
cluding
hirsutism
; male-pattern baldness;
disruption or cessation of
menstruation
;
enlargement of the
clitoris
; loss of nor-
mal
fat deposits around the
hips;
development of the arm and shoulder
muscles; and deepening of the voice.
virility A term used to describe the
quality of maleness, especially in sexual
characteristics and performance.
virilization The development in a woman
of male characteristics as a result of
overproduction of
androgen hormones
by the adrenal glands and/or ovaries.
This may be due to various conditions
such as certain
adrenal tumours
, poly-
cystic ovary (see
ovary, polycystic
) and
some other
ovarian cysts
, or congenital
adrenal hyperplasia
.
virion A single, complete,
virus
particle.
virology The study of
viruses
and the
epidemiology
and treatment of diseases
caused by viruses. In a more restricted
sense, virology also refers to the isola-
tion and identification of viruses to
diagnose specific viral infections. Depend-
ing on the type of virus, this may involve
growing viruses in cultures of human or
animal cells,
staining
or microscopic
examination of specimens containing
viruses, or
immunoassay
techniques.
virulence The ability of a microorganism
to cause disease. This can be assessed
by measuring what proportion of the
population exposed to the microorgan-
ism develops symptoms of disease, how
rapidly the infection spreads through the
body, or the mortality from the infection.
viruses The smallest known types of
infectious agent. It is debatable whether
viruses are truly living organisms or just
collections of molecules capable of self-
replication under specific conditions.
Their sole activity is to invade the cells
of other organisms, which they then
take over to make copies of themselves.
Outside living cells, viruses are inert.
A single virus particle (virion) consists
of an inner core of
nucleic acid,
which
may be either
DNA
or
RNA
, surrounded
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