HYPERPLASIA
HYPERTENSION
H
The condition is diagnosed by
X-rays
of
the hands and skull and by
blood tests
.
Surgical removal of abnormal parathyroid
tissue usually cures the condition. If the
remaining tissue is unable to produce
enough parathyroid hormone, treatment
for
hypoparathyroidism
is required.
hyperplasia
Enlargement of an organ
or tissue due to an increase in the
number of its cells. The new cells are
normal, unlike those of a tumour. Hyper-
plasia is usually the result of hormonal
stimulation.
It may
occur normally
(such as in the enlargement of breast
tissue in pregnancy) or it may indicate a
disorder. (See also
hypertrophy
.)
hyperplasia,
gingival
Abnormal en-
largement of the gums. Causes include
gingivitis
,
persistent breathing through
the mouth, the anticonvulsant drug
phenytoin
,
and ill-fitting dentures. Sur-
gical treatment may be needed.
hyperpyrexia
A term
for extremely
high body temperature.
hypersensitivity
Overreaction of the
immune system
to an
antigen
.
There are
4 main types of hypersensitivity.
Type I is associated with
allergy
. After
a first exposure to an antigen,
antibod-
ies
are formed; these coat cells called
mast cells in various tissues. On second
exposure, the antigen and antibodies
combine, causing the mast cells to dis-
integrate and release chemicals that
cause the symptoms of
asthma
, allergic
rhinitis
,
urticaria
,
anaphylactic shock
,
or
other allergic illnesses.
In type II reactions, antibodies that
bind to antigens on cell surfaces are
formed, leading to possible destruction
of the cells. Type II reactions may lead
to certain
autoimmune disorders
.
In type III reactions, antibodies com-
bine with antigens to form particles
called immune complexes. These lodge
in various tissues and activate further
immune system responses, leading to
tissue damage. This type of reaction is
responsible for
serum sickness
and for
the lung disease allergic
alveolitis
.
In type IV reactions, sensitized
T-lym-
phocytes
(a class of white
blood cell
) bind
to antigens and release chemicals called
lymphokines, which promote an inflam-
matory reaction. Type IV reactions are
responsible for
contact dermatitis
and
measles
rash; they may also play a part
in “allergic” reactions to drugs.
Treatment of hypersensitivity depends
on the type, cause, and severity. When
possible, exposure to the offending anti-
gen should be avoided.
hypersplenism
An overactivity of the
spleen
resulting in, and associated with,
blood disease. One of the functions of
the spleen is to break down
blood cells
as they age and wear out. An overactive
spleen may begin to destroy cells indis-
criminately, causing a deficiency of any
of the types of blood cell. In most cases,
the spleen will also be enlarged. Hyper-
splenism may be primary, occurring for
no known reason, but more commonly
it is secondary to another disorder in
which the spleen has become enlarged,
such as
Hodgkin's disease
or
malaria
.
Hypersplenism causes
anaemia
and
thrombocytopenia
, and there may be a
decrease in resistance to infection. Pri-
mary hypersplenism is treated with
splenectomy
. Treatment of secondary
hypersplenism aims to control the cause.
hypertension
Persistently raised
blood
pressure
exceeding about 140 mmHg
(systolic) and 90 mmHg (diastolic) at rest.
Hypertension is very common, particu-
larly in men, and its incidence is highest
in middle-aged and elderly people.
Hypertension is usually symptomless
but may cause headaches and visual
disturbances when severe. It increases
the risk of
stroke
,
coronary artery disease
,
and
heart failure
,
and may eventually
lead to kidney damage and
retinopathy
.
In many cases, there is no obvious
cause. Factors associated with hyper-
tension include high alcohol intake, a
high-salt diet, obesity, a family history
of the condition, a sedentary lifestyle, a
high degree of stress, and smoking.
Specific causes include various
kidney
disorders, certain disordes of the
adre-
nal glands
,
pre-eclampsia
,
coarctation of
the aorta
, and use of certain drugs. Tak-
ing the combined
contraceptive
pill can
increase the risk.
With mild to moderate hypertension,
if no underlying cause is found, lifestyle
changes are recommended, for exam-
ple, introducing regular exercise and
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