Bma Illustrated Medical Dictionary

Loss of sex drive and a reduction in the
size of the testes are often the first signs.
Excess iron over a period of time causes
liver enlargement and cirrhosis, and can
lead to diabetes mellitus, bronzed skin
coloration, cardiac arrhythmia, and, even-
tually, liver failureand liver cancer.
Diagnosis is based on blood testsand
a liver biopsy. Treatment is by regular
venesection. (See also haemosiderosis.)
haemodialysisOne of the 2 means of
dialysisused to treat kidney failure.
haemoglobinThe oxygen-carrying pig-
ment that is present in red blood cells.
Haemoglobin molecules, which are pro-
duced by bone marrow,are made up of
4 protein chains (2 alpha- and 2 beta-
globin) and 4 haem (a red pigment that
contains iron).

Oxygen from the lungs enters red

blood cells in the bloodstream. The oxy-

gen then combines chemically with the

haem within the haemoglobin to form

oxyhaemoglobin, which gives blood in

the arteries its distinctive bright red

colour and is carried around the body.

In areas that need oxygen, the oxyhaem-

oglobin releases its oxygen and reverts

to haemoglobin, giving blood in the

veins its distinctive darker colour.

Some defects in haemoglobin produc-

tion result from a genetic disorder; such

defects are subdivided into errors of

haem production, known as porphyrias,

and those of globin production, known

HAEMOGLOBIN

as haemoglobinopathies. Other defects,

such as some types of anaemia, have a

nongenetic cause.

haemoglobinopathyA term used to

describe the genetic disorders in which

there is a fault in the production of the

globin chains of haemoglobin. Examples

of haemoglobinopathies include sickle

cell anaemiaand the thalassaemias.

haemoglobinuriaThe presence in the

urine of haemoglobin. Haemoglobin is

mainly contained in red blood cells, but a

small amount is free in the blood plas-

ma. Excessive breakdown of red blood

cells, which may be due to heavy exer-

cise, cold weather, falciparum malaria,

or haemolytic anaemia, increases the

concentration of free haemoglobin in

the plasma. The excess haemoglobin is

excreted in the urine.

haemolysisThe destruction of red blood

cells. Haemolysis is the normal process

by which old red blood cells are

destroyed, mainly in the spleen. Biliru-

bin, a waste product of haemolysis, is

excreted into the bileby the liver.

Abnormal haemolysis, in which red

blood cells are destroyed prematurely,

may cause anaemia and jaundice (see

anaemia, haemolytic).

haemolytic anaemiaSee anaemia, hae-

molytic.

haemolytic disease of the newborn

Excessive haemolysis(destruction of

red blood cells) in the fetus and new-

born by antibodies produced by the

mother. Haemolytic disease of the new-

born is most often caused by Rhesus

incompatibility. This occurs when a moth-

er with Rh-negative type blood, who has

previously been exposed to Rh-positive

blood through birth, miscarriage, abor-

tion, or amniocentesis, is pregnant with

a baby that has Rh-positive blood.

Haemolytic disease has become un-

common since the introduction of routine

preventative treatment for Rh-negative

women during pregnancy (see anti-D

(Rh 0 ) immunoglobulin).

In mild cases of haemolytic disease,

the newborn baby becomes slightly jaun-

diced during the first 24 hours of life

(due to excess bilirubin in the blood)

and slightly anaemic. In more severe

cases, the level of bilirubinin the blood

HAEMODIALYSIS HAEMOLYTIC DISEASE

H

Beta-globin

chain

Haem

Iron

STRUCTURE OF HAEMOGLOBIN

Alpha-globin

chain