MEDICINE Study Guide - Final Guide: Sickle-Cell Disease, Microcirculation, Valine
9 Nov 2022
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Sickle cell anemia is a hereditary type of chronic hemolytic anemia. Transmitted as a mendelian dominant, nongenderlinked characteristic. A concordance exists between the prevalence of malaria and hbs. The name is derived from the peculiar microscopic appearance of sickle-or crescent-shaped erythrocytes found in the circulating blood. Normal adult hemoglobin (hba) is genetically altered to produce sickle hemoglobin (hbs) by the substitution of valine for glutamine at the sixth position of the -globin chain. In the heterozygote-only about 40% of the hemoglobin is hbs, so that the individual has only the sickle-cell trait and manifests clinical evidence of sickling only under conditions of severe hypoxia. In the homozygote-nearly all hemoglobin is hbs, and the individual suffers from sickle cell anemia. The rbcs with sickle shape become much less deformable; therefore, obstructing the microcirculation and thus caused tissue hypoxia, further promotes sickling. Sickle-shaped rbcs are rapidly hemolyzed and have a life span of only about 10 20 days.
