H 2 -receptor antagonistsA common
abbreviation for histamine 2 -receptor ant-
agonists, a group of ulcer-healing drugs.
(See also cimetidine; ranitidine; famotidine.)
habituationThe 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).
haemA compound that contains iron
and which combines with globin to
form haemoglobin.
haem-A prefix indicating blood.
haemangioblastomaA 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, nystagmusand, if the
tumour is in the cerebellum, ataxia. Most
can be removed surgically.
haemangiomaA 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.
haemarthrosisBleeding 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 Fluid may be withdrawn for pain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. Haemophiliacsare given factor VIIIto promote blood
clotting. Resting the joint in an elevated
position can prevent further bleeding.
Repeated haemarthrosis may damage
joint surfaces, causing osteoarthritis.
haematemesisThe medical term for
vomiting blood.
haematologyThe study of bloodand
its formation, as well as the investiga-
tion and treatment of disorders that
affect the blood and the bone marrow.
haematomaA 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 aurisThe medical term
for cauliflower ear.
haematuriaBlood 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 tractdisorder 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. Bleedingdisor-
dersmay 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-
venousurography can help determine
the cause. If bladder disease is suspect-
ed, cystoscopyis performed.
haemochromatosisAn 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.H 2 -RECEPTOR ANTAGONISTS HAEMOCHROMATOSISH