Sickle cell anemia is characterized by: September 2010

Ans. D: Autosplenectomy Sickle cell anemia causes autosplenism by causing hypoxia and infarcts in the spleen. Since in the spleen blood flow is sluggish, the oxygen tension is low. When red blood cells with hemogblobin S are exposed to this low oxygen tension they tend to aggregate and polymerize. Sickled cells also express more adhesion molecules and appear more sticky. The sickle cells arrest in the hypoxic vascular bed in the spleen, resulting in a vicious cycle: decrease in 02, sickling and vascular obstruction from thrombus formation. Initially the spleen is enlarged, then progressively becomes smaller. The stasis of flow in the spleen causes hypoxic damage, thrombosis, infarction and fibrosis. In the end the spleen "disappears" completely (termed 'autosplenectomy').