I
Iron-deficiency anaemia is caused by a
deficiency of iron, an essential cons-
tituent of haemoglobin.
CAUSES
The commonest cause of iron-defici-
ency anaemia is iron loss due to heavy
or persistent bleeding; the most com-
mon cause in women of childbearing
age is particularly heavy periods (see
menorrhagia).
Pregnancy stops menstru-
al losses, but the baby is an even greater
drain on maternal iron stores. Other
causes include blood loss from the
digestive tract due to disorders such as
erosive
gastritis,
peptic ulcer, stomach
cancer, inflammatory bowel disease, haem-
orrhoids,
and bowel tumours (see
colon,
cancer of).
Prolonged use of aspirin and
other
nonsteroidal anti-inflammatory drugs
(NSAIDs)
can
cause
gastrointestinal
bleeding. In some countries,
hookworm
infestation
of the digestive tract is an
important cause
of anaemia.
Rarely,
bleeding may also occur as a result of
disorders of the urinary tract (such as
kidney tumours
or
bladder tumours).
Iron deficiency may also be caused or
worsened by lack of iron in, or its poor
absorption from, the diet. Malabsorption
of iron may have various causes, includ-
ing the removal of part or all of the
stomach (see
gastrectomy)
or
coeliac dis-
ease
(a disorder that impairs digestion).
SYMPTOMS
The symptoms of iron-deficiency anae-
mia are those of the underlying cause,
along with a sore mouth or tongue; and
those that are common to all forms of
anaemia, such as fatigue, headaches,
and breathlessness.
DIAGNOSIS AND TREATMENT
Diagnosis is made from a
blood count
that reveals the red blood cells to be
microcytic (abnormally small). Meas-
urement of the iron levels in the blood
confirms
the
diagnosis
but
further
investigation will be needed to establish
the underlying cause. Treatment is given
for the underlying cause, along with a
course of iron tablets or, very rarely,
iron injections in order to build up the
depleted iron stores.
anaemia, megaloblastic
A major type of
anaemia
(a reduced
level of the oxygen-carrying pigment
haemoglobin in the blood). Megalo-
blastic anaemia is caused by deficiency
of vitamin B12 or another vitamin, folic
acid. Either of these deficiencies seri-
ously interferes with the production of
red blood cells in the bone marrow. An
ANAESTHESIA
Bone marrow in megaloblastic anaemia
In this microscopic view, some of the large cells are
abnormal red-cell precursors (megaloblasts).
excess of cells known as megaloblasts
(abnormal immature red cells) appears
in the marrow. Megaloblasts give rise to
enlarged and deformed red blood cells
known as macrocytes.
CAUSES
Vitamin B
12
deficiency
Vitamin B12 is
found only in foods of animal origin,
such as meat and dairy products. It is
absorbed from the small intestine by
first combining with intrinsic factor, a
chemical produced by the stomach
lining. The most common cause of vita-
min B12 deficiency is
pernicious anaemia
in which the stomach lining fails to pro-
duce intrinsic factor, usually as a result
of an
autoimmune disorder
(in which the
immune system attacks the body’s own
tissues). Total gastrectomy (removal of
the stomach) also prevents the produc-
tion of intrinsic factor, and removal of
part of the small intestine prevents B12
absorption, as does the intestinal dis-
order
Crohn’s disease.
In a minority of
cases, vitamin B12 deficiency is due to a
vegan diet (which excludes all foods of
animal origin).
Folic acid deficiency
Folic acid is found
mainly in green vegetables and liver. The
usual cause of deficiency is a poor diet.
It can also be caused by anything that
interferes with absorption of folic acid
from
the
small
intestine
(Crohn’s
disease or
coeliac disease,
for example).
Folic acid is required by rapidly dividing
cells, as in the fetus. Women are advised
to take folic acid supplements before
conception and in early pregnancy,
although this is to reduce the risk of the
fetus having a
neural tube defect
rather
than to prevent anaemia.
SYMPTOMS
Many people with mild megaloblastic
anaemia have no symptoms. Others may
experience tiredness, a sore mouth and
tongue, weight loss, and mild
jaundice.
If B12 deficiency continues for a long
time, additional symptoms as a result of
nerve damage, including numbness and
tingling in the feet, may develop.
DIAGNOSIS AND TREATMENT
Megaloblastic anaemia is diagnosed by
blood tests
and confirmed if a
bone
marrow biopsy
(removal of a small sam-
ple of marrow for microscopic analysis)
reveals the presence of large numbers of
megaloblasts.
Megaloblastic
anaemia
caused
by
poor diet can be remedied with a short
course of vitamin B12 injections or folic
acid tablets and the introduction of a
normal diet. A lifelong course of vita-
min B12 injections or folic acid tablets is
required if the underlying cause of mal-
absorption is incurable.
anaemia, pernicious
See
pernicious anaemia.
anaemia, sickle cell
See
sickle cell anaemia
.
anaerobic
Capable
of living,
functioning,
and
growing without oxygen. Many bacteria
are anaerobes and thrive in the intesti-
nal canal or in tissue that has a poor
supply of oxygenated blood.
Some human body cells are capable
of limited
anaerobic
activity. When
muscular exertion is so strenuous that
oxygen is used faster than the blood
circulation can supply it (during sprint-
ing, for example), the muscle cells can
temporarily work anaerobically. When
this happens, lactic acid is produced as a
waste product (instead of the carbon
dioxide that is produced from
aerobic
activity). This acid buildup can cause
muscle fatigue and pain, thereby limit-
ing
the
time
for
which
anaerobic
activity can be carried out. Compensa-
tion for this anaerobic activity requires
oxygen to convert the lactic acid to
glucose or to carbon dioxide, which
explains the need to continue to breathe
rapidly following vigorous exertion. The
deficit of oxygen that builds up in the
muscles during exercise is known as the
oxygen debt.
anaesthesia
The absence of all sensation; insensib-
ility. The term most commonly refers to
anaesthesia that is induced artificially
for medical purposes.
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