Anemia
A condition marked by the presence of an abnormally
low number of red blood cells or hemoglobin molecules,
the iron-containing compound in red blood cells that
transports oxygen. There are many different types of
anemia, each one with its own cause. As a group, anemias
are the most common disease affecting the blood.
In the healthy person, red blood cells are produced
in the bone marrow and have a life span of approximately
120 days, at which point new red blood cells replace
them. In healthy individuals, the formation of new red
blood cells balances the destruction of old cells, and
the amount of hemoglobin remains steady within the normal
range. Anemia can result if red blood cells are destroyed
prematurely, if the bone marrow loses the ability to
make a sufficient number of new red blood cells, or
if a person experiences blood loss from bleeding. The
net result is a deficiency in red blood cells or hemoglobin.
This loss in the body's ability to transport oxygen
produces the symptoms of anemia.
Symptoms
Most anemias start with mild symptoms that may hardly
be noticed. Symptoms worsen as the disease progresses.
A person with anemia may feel fatigue and appear paler
than usual. The pallor is more apparent in the nail
beds of the fingers and toes, the insides of the lips
and eyelids, and the palms, where the creases may become
as pale as the skin surrounding them. The heart rate
often increases as the heart works harder to pump blood
throughout the body in an effort to compensate for the
oxygen deficit. Shortness of breath when exercising
may also occur.
Types
The most common cause of anemia is iron deficiency.
Since iron is an essential component of hemoglobin,
an iron deficiency leaves the body unable to produce
enough hemoglobin to meet its needs. The usual causes
of iron-deficiency anemia are inadequate diet, poor
absorption of iron from food, and blood loss. In the
United States, blood loss is the most common cause of
iron deficiency in adults, which may be caused by conditions
such as ulcers, colon polyps, colon cancer or by the
use of nonsteriodial anti-inflammatory drugs (NSAIDs).
Insufficient vitamin B12 causes pernicious
anemia. Insufficient folic acid produces a folic
acid deficiency anemia. Since vitamin B12 and folate
are important building blocks for red blood cells, insufficient
vitamin B12 or folic acid results in an inability of
the bone marrow to produce enough new red blood cells
to replace old ones.
Hemolytic anemias involve disease processes in which
red blood cells break down faster than bone marrow can
produce them. The most common cause of hemolytic anemia
is an acquired to one's own red blood cells. Antibodies
attack the cells as if they are foreign to the body
and subsequently destroy them. Hemolytic anemia can
also develop as a result of taking certain medications
and from an inherited defect in enzymes such as glucose-6-phosphate
dehydrogenase (G6PD).
In the aplastic anemias, the bone marrow fails to
properly develop all types of blood cells, including
red blood cells.
Certain inherited anemias involve genetic abnormalities
that cause the body to manufacture defective hemoglobin.
Examples include sickle cell anemia and the thalassemias.
Many infections and chronic diseases occur in conjunction
with anemia. Anemias that occur along with a chronic
disease are relatively common and probably result from
a combination of factors, including a decrease in the
ability of the bone marrow to produce red blood cells,
a shortened red blood cell life span, and impaired iron
utilization. Examples of causative disease include endocarditis
(inflammation of the lining of the heart that usually
involves the heart valves), osteomyelitis (inflammation
of the bones), juvenile rheumatoid arthritis, rheumatic
fever, Crohn's disease and ulcerative colitis.
Source: AMA Complete Medical Encyclopedia,
Copyright 2003, American Medical Association
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