m a la b s o r p t io n
certain liver disor-
ders, and in premature infants. It leads
to the destruction of red blood cells,
w hich eventually leads to
a n a e m ia
infants, it causes irritability and
o e d e m a
(accumulation of fluid in tissues).
Prolonged excessive intake of vitamin E
may cause abdominal pain, nausea, and
diarrhoea. It may also reduce intestinal
absorption of vitamins A, D, and K.
v ita m in K
A fat-soluble
v ita m in
that is essential for
the formation in the liver of substances
that promote blood clotting. Green veg-
etables, vegetable oils, egg yolk, cheese,
pork, and liver are good sources of vita-
m in K, w hich is also manufactured by
bacteria in the intestine.
Dietary deficiency of vitamin K rarely
occurs. Deficiency may develop in peo-
m a la b s o r p t io n
disorders, or chronic diarrhoea. It may
also result from prolonged treatment
a n t ib io t ic d r u g s
Newborn babies
lack the intestinal bacteria that produce
vitamin K and are routinely given sup-
plements to prevent deficiency. Vitamin
K deficiency may cause nosebleeds and
bleeding from the gums, intestine, and
urinary tract. In rare, severe cases, brain
haemorrhage may result.
Excessive intake of vitamin K is not
known to cause harmful effects.
v ita m in s u p p le m e n ts
A group of dietary preparations con-
taining one or more
v it a m in s
multivitamin preparations also contain
m in e r a ls
such as iron and calcium. A
healthy person with a balanced diet
should not need to take supplements
n u t rit io n
) .
Excessive doses of certain
vitamins (especially vitamins A, B6, and
D) may actually be harmful.
Vitamin supplements may be given in
order to prevent vitamin deficiency in
susceptible people, including those in -
dividuals with increased requirements
(such as women who are pregnant or
breast-feeding); those people who fol-
low a restricted diet (such as
v e g a n is m
) ;
those who have severe
a lc o h o l d e p e n -
d e n c e
and those people suffering from
disorders that may cause vitamin defi-
m a la b s o rp t io n
some liver and kidney disorders.
Vitamin supplements are also used
in the treatment of certain disorders,
including diagnosed vitamin deficiency.
For example, vitamin D is used to treat
the bone condition
o s te o m a la c ia
vitamin A derivatives are given in the
treatment of severe
a c n e
tary vitamins may be given orally or
may be injected (as is the case with vit-
amin B12 and vitamin K).
v itilig o
A common disorder of
s k in
tion in w hich patches of skin, most
commonly on the face, hands, armpits,
and groin, lose their colour. Vitiligo is
thought to be an
a u t o im m u n e d is o r d e r
(in w hich the body’s immune system
attacks its own tissues). The condition
may occur at any age, but it usually
develops in early adulthood.
Spontaneous repigmentation occurs
in some cases. A course of
p h o t o t h e ra p y
can also induce repigmenta-
tion of the skin, and creams containing
c o r t ic o s t e r o id d ru g s
may help.
Vitiligo affecting the hands
Loss of pigment is the only skin change that occurs.
The usual remedyfor the condition isto maskthe
white patches with cosmetics.
v itre o u s h a e m o rrh a g e
Bleeding into the
v itre o u s h u m o u r
gel-like substance that fills the main
cavity of the eye. A common cause of a
vitreous haemorrhage is diabetic
r e t in -
o p a th y
in w hich new,
fragile blood
capillaries form on the retina. Vitreous
major haemorrhage causes poor vision
until the blood is reabsorbed, w hich
may not be for several months, if at all.
v itre o u s h u m o u r
The transparent, gel-like body that fills
the rear compartment of the
ey e
the crystalline lens and the retina. The
vitreous hum our is composed almost
entirely of water.
v iv is e c tio n
The performance of a surgical operation
on a live animal, particularly for the
purposes of research. (See also
a n im a l
e x p e rim e n t a t io n
. )
v o c a l c o rd s
Two fibrous sheets of tissue in the
la ry n x
voice production. The vocal cords are
attached at the front to the thyroid car-
tilage and at the rear to the arytenoid
cartilages (see
L o c a tio n o f th e v o c a l c o rd s
box, overleaf).
In order to produce sound, the vocal
cords (which normally form a V-shaped
opening) close and vibrate as air that is
expelled from the lungs passes between
them. Alterations in cord tension pro-
duce sounds of different pitch, which
are modified by the tongue, mouth, and
lips to form speech
v o ic e b o x
la ry n x
v o ic e , lo s s o f
Inability to speak normally. Temporary
partial loss of voice commonly results
from straining of the muscles of the
la r-
y n x
(voicebox) through overuse of the
voice or from inflammation of the
v o c a l
c o r d s
la r y n g it is
Persistent or recurrent loss of voice
may be the result of
p o ly p s
on the vocal
cords, thickening of the vocal cords
h y p o t h y ro id is m
(underactivity of the
thyroid gland), or interference with
the nerve supply to the larynx muscles
as a result of cancer of the larynx,
th y -
r o id g la n d
o e s o p h a g u s
Total loss of
voice is rare and is usually of psycho-
h o a r s e n e s s
la ry n x, d is o r d e r s o f
) .
V o lk m a n n ’s c o n tra c tu re
A disorder of the wrist and fingers in
w hich they become permanently fixed
in a bent position.
Volkmann’s contracture occurs because
of an inadequate blood supply to the
forearm muscles that control the wrist
and fingers. This is most likely to be the
result of an injury.
numb, and white or blue. Finger move-
ments are weak and painful, and there
is no pulse at the wrist. Unless treat-
ment is started within a few hours,
wrist and finger deformity develops.
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