Biology of Disease

SUMMARY

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13.10 Summary

The blood system has many components, erythrocytes, leukocytes and
platelets suspended in the complex protein rich plasma. Hemoglobin
transports oxygen from the lungs to the tissues. Anemia results when the
Hb level decreases and this is usually accompanied with a reduction in the
erythrocyte count. Anemias may be associated with normal sized erythrocytes
or ones that are microcytic or macrocytic, depending upon the cause.

Many hundreds of mutations are known that affect Hb giving rise to
hemoglobinopathies. These range from relatively mild conditions to ones
that are severe and life-threatening. In sickle cell anemia, the molecules of
deoxyhemoglobin aggregate to form fibrils, which distort the erythrocytes,
making them less flexible when passing through the capillaries. This leads
to a lack of oxygen in the tissues, severe pain and hemolysis. It is due to a
point mutation in the gene for B-globin. Thalassemias are a group of relatively
common hemoglobinopathies, caused by the defective synthesis of the A- or
B-globins. Thalassemias, again, vary from the relatively mild to very severe,
depending upon the precise defect.

The commonest blood disease is glucose 6-phosphate dehydrogenase
deficiency. Typically this is asymptomatic until the patient takes a particular
drug that produces an excessive demand for glutathione in the erythrocytes
and this leads to a severe hemolytic anemia.

Many defects of the blood clotting system are known. The commonest is
hemophilia A, which is caused by lack of Factor VIII, one of the protein factors
active in the clotting mechanism.

QUESTIONS

1. Which of the following statements about iron-deficiency anemia is/are
   true?

(a) The erythrocytes are small and hypochromic.

(b) The serum iron-binding capacity falls.

(c) There is angular stomatitis and brittle hair.

(d) Deposits of hemosiderin will be found in the liver and spleen.

(e) The erythrocytes are microcytic in appearance.

2. Identify the blood cells, A and B, in the accompanying figure.