H
H
H
2
-receptor antagonists
A common
abbreviation for histamine
2
-receptor ant-
agonists, a group of
ulcer-healing drugs.
(See also
cimetidine; ranitidine; famotidine.)
habituation
The process of becoming
accustomed to an experience. In general,
the more a person is exposed to a stim-
ulus, the less he or she is affected by it.
People can become habituated to certain
drugs and develop a reduced response
to their effects (see
tolerance
).
haem
A compound that contains iron
and which combines with globin to
form
haemoglobin
.
haem-
A prefix indicating
blood.
haemangioblastoma
A rare type of brain
tumour consisting of blood-vessel cells.
Haemangioblastomas develop slowly as
cysts, often in the cerebellum, and are
mostly noncancerous. Symptoms include
headache, vomiting,
nystagmus
and, if the
tumour is in the cerebellum,
ataxia.
Most
can be removed surgically.
haemangioma
A birthmark caused by
abnormal distribution of blood vessels.
Types of haemangioma include
port-
wine stains
,
stork marks
, and
strawberry
naevi
. They generally disappear without
leaving a scar by 5-7 years.
Haemangiomas do not usually require
treatment. However, a haemangioma
that bleeds persistently or that looks
unsightly may need to be removed, by
laser treatment
,
cryosurgery
,
radiothera-
py
,
embolization
, or
plastic surgery
.
haemarthrosis
Bleeding into a
joint,
causing the capsule that encloses the
joint to swell, and resulting in pain and
stiffness. Haemarthrosis is usually the
result of severe injury to a joint. Less
common causes are
bleeding disorders
,
such as
haemophilia
, and overuse of
anticoagulant drugs
.
Ice-packs
may reduce swelling and
pain. Fluid may be withdrawn for pain
relief and for diagnosis. Haemophiliacs
H
2
-RECEPTOR ANTAGONISTS
are given
factor VIII
to promote blood
clotting. Resting the joint in an elevated
position can prevent further bleeding.
Repeated haemarthrosis may damage
joint surfaces, causing
osteoarthritis
.
haematemesis
The medical term for
vomiting blood
.
haematology
The study of
blood
and
its formation, as well as the investiga-
tion and treatment of disorders that
affect the blood and the
bone marrow
.
haematoma
A localized collection of
blood
(usually clotted) that is caused by
bleeding from a ruptured blood vessel.
Haematomas can occur almost any-
where in the body and vary from a
minor to a potentially fatal condition.
Less serious types of haematoma in-
clude haematomas under the nails or in
the tissues of the outer ear (
cauliflower
ear
). Most haematomas disappear with-
out treatment in a few days, but if they
are painful they may be drained. More
serious types include extradural and
subdural haematomas, which press on
the brain (see
extradural haemorrhage
;
subdural haemorrhage
).
haematoma auris
The medical term
for
cauliflower ear
.
haematuria
Blood in the
urine
, which
may or may not be visible to the naked
eye. In small amounts, it may give the
urine a smoky appearance.
Almost any
urinary tract
disorder can
cause haematuria.
Urinary tract infection
is a common cause;
prostatitis
may be a
cause in men.
Cysts
,
kidney tumours
,
bladder tumours
, stones (see
calculus,
urinary tract
), and
glomerulonephritis
may cause haematuria.
Bleeding disor-
ders
may also cause the condition.
Blood that is not visible to the naked
eye may be detected by a dipstick
urine
test
or microscopic examination.
CT
scanning
,
ultrasound scanning
, or intra-
venous
urography
can help determine
the cause. If bladder disease is suspect-
ed,
cystoscopy
is performed.
haemochromatosis
An inherited dis-
ease in which too much dietary iron is
absorbed.
Excess iron gradually ac-
cumulates in the liver, pancreas, heart,
testes, and other organs. Men are more
frequently affected because women reg-
ularly lose iron in menstrual blood.
HAEMOCHROMATOSIS
262
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