Sickle-cell Disease

The most common hemoglobin of adult humans is known as hemoglobin A (HbA). However, other variant forms of hemoglobin are found in some humans. One of these is called hemoglobin S (HbS). Individuals who manufacture HbS exclusively suffer from sickle-cell disease.

Sickle-cell disease is quite common in malaria-ridden parts of Africa and Asia and also occurs in African-Americans and others descended from inhabitants of those regions.

Red blood cells of a

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Animal Circulatory Systems

An efficient circulatory system has:

  • a fluid, e.g., blood, to carry the materials to be transported;
  • a system of vessels to distribute the blood;
  • a pump to push the blood through the system;
  • exchange organs to carry out exchanges between the blood and external environment, e.g.,