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Sickle Cell Anemia (Visit Resource)
Introduction Sickle Cell Anemia (SCA) is caused by a change in the chemical composition of the protein (hemoglobin or Hgb) that carries the oxygen inside of the red blood cells (RBC's). Normal Hgb is a round or ball-shaped folded molecule composed of 4 protein subunits - 2 alpha chains and 2 beta chains. The chemical change is a valine amino acid substituted for glutamic acid in both of the beta chains (HbSS). These chemical changes in hemoglobin cause the shape of the molecule to change under certain conditions such as lowered oxygen concentration and dehydration. Deoxygenated HgSS molecules can chemically link to each other, creating chains of molecules - a polymer. In turn, these abnormal elongated hemoglobin polymer structures distort the shape of the whole red blood cell. The abnormal RBC's can damage the vessels around them and the tissues that depend on the vessels for oxygen and nourishment. For example, the damaged RBC's can cause thrombosis (clotting) and then secondary ischemic damage to the adjacent and surrounding tissues - causing infarction (cellular death). (more information and images)
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Added: Mon Jan 01 2007
