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P A R T 8
Drugs acting on the cardiovascular system
if the body does not have enough of the building blocks
necessary to form RBCs or if a person has a genetic
predisposition to forming abnormal, as in sickle cell
anaemia. To produce healthy RBCs, the bone marrow
must have the following:
• Adequate amounts of iron, which are used in forming
haemoglobin rings to carry the oxygen.
• Minute amounts of vitamin B
12
and folic acid, to form
a strong supporting structure that can survive being
battered through blood vessels for 120 days.
• Essential amino acids and carbohydrates to complete
the haemoglobin rings, cell membrane and basic
structure.
Normally, an individual’s diet supplies adequate
amounts of all of these substances, which are absorbed
from the gastrointestinal (GI) tract and transported
to the bone marrow. However, when the diet cannot
supply enough of a nutrient, or enough of the nutrient
cannot be absorbed, the person can develop a deficiency
anaemia. Fewer RBCs are produced, and the ones that
are produced are immature and inefficient iron carriers.
This type of anaemia is called a deficiency anaemia.
Another type of anaemia is megaloblastic anaemia,
which involves decreased production of RBCs and
ineffectiveness of those RBCs that are produced (they do
not usually survive for the 120 days that is normal for
the life of an RBC). People with megaloblastic anaemia
usually have a lack of vitamin B
12
or folic acid.
A third type of anaemia is haemolytic anaemia,
which involves a lysing of RBCs because of genetic
factors or from exposure to toxins. Sickle cell anaemia is
a type of haemolytic anaemia.
Iron-deficiency anaemia
All cells in the body require some amount of iron, but
iron can be very toxic to cells, especially neurons. To
maintain the needed iron levels and avoid toxic levels,
the body has developed a system for controlling the
amount of iron that can enter the body through intesti-
nal absorption. Only enough iron is absorbed to replace
the amount of iron that is lost each day. Once iron is
absorbed, it is carried by a plasma protein called trans-
ferrin, a beta-globulin. This protein carries iron to
various tissues to be stored and transports iron from
RBC lysis back to the bone marrow for recycling.
Only about 1 mg of iron is actually lost each day in
sweat, in sloughed skin, and from GI and urinary tract
linings. Because of the body’s efficient iron recycling,
very little iron is usually needed in the diet, and most
diets adequately replace the iron that is lost. However,
in situations in which blood is being lost, a negative
iron balance might occur, and the person could develop
iron-deficiency anaemia
. This can occur in certain rare
GI diseases in which the person is unable to absorb iron
from the GI tract, but iron-deficiency anaemia is also a
relatively common problem in certain groups, including
the following:
• Menstruating women, who lose RBCs monthly
• Pregnant and breastfeeding women, who have
increased demands for iron
• Rapidly growing adolescents, especially those who do
not have a nutritious diet
• Persons with GI bleeding, including individuals with
slow bleeding associated with use of non-steroidal
anti-inflammatory drugs (NSAIDs)
The person with this type of anaemia may complain of
being tired because there is insufficient oxygen delivery
to the tissues. These conditions are usually treated
with iron replacement therapy (see section on iron
preparations).
Megaloblastic anaemias
Megaloblastic anaemias
result from insufficient
amounts of folic acid or vitamin B
12
to adequately create
the stromal structure needed in a healthy RBC, causing
a slowing of nuclear DNA synthesis. This effect occurs
in rapidly dividing cells such as the bone marrow. The
bone marrow contains a large number of megaloblasts,
or large, immature RBCs, and because these RBCs are
so large, they become crowded in the bone marrow
and fewer RBCs are produced, increasing the amount
of immature cells in circulation. Cells in the GI tract
are additional examples of cells that are often affected.
When the GI tract is involved, this can result in the
appearance of a characteristic red and glossy tongue,
and diarrhoea.
Folic acid deficiency
Folic acid is essential for cell division in all types of
tissue. Deficiencies in folic acid are noticed first in
rapidly growing cells, such as those in cancerous tissues,
in the GI tract and in the bone marrow. Folic acid is
very important for the developing fetus, a site of very
rapidly growing cells. Pregnant women are urged to
take folic acid supplements to help prevent fetal abnor-
malities, particularly neural tube defects. Most people
can get all the folic acid they need from their diet. For
example, folic acid is found in green leafy vegetables,
milk, eggs and liver. Deficiency in folic acid may occur in
certain malabsorption states, such as sprue and coeliac
diseases. Malnutrition that accompanies alcoholism is
also a common cause of folic acid deficiency. Repeated
pregnancies and extended treatment with certain anti
epileptic medications can also contribute to folic acid
deficiency. Folic acid deficiency is treated by the admini
stration of folic acid or folate.
Vitamin B
12
deficiency
Vitamin B
12
is used in minute amounts by the body and
is stored for use if dietary intake falls. It is necessary
