Platelets

The platelets, or thrombocytes, are small, irregularly-shaped cells in the blood which lack nuclei. They are about 3 µm in diameter and there are about 3 lakhs/µL of them in the circulating blood. The platelets are formed by fragmentation of the cytoplasm of the megakaryocytes in the bone marrow and released into the blood. The megakaryocytes are giant cells formed from the haemopoietic stem cells. The average lifespan of a platelet is between 8 days (half-life is 4 days) and is then destroyed mostly in the spleen.

Functions

The platelets play an important role in achieving temporary haemostasis by aggregating to form platelet plugs at the sites of injury.

Platelet disorders

The normal platelet count is 1.5 to 4 lakhs/µL (1.5 to 4 lakhs/cmm). A platelet count below 1 lakh is called thrombocytopenia. It can result from decreased production in the bone marrow, sequestration of platelets in an enlarged spleen or due to increased destruction. The platelet count below which spontaneous bleeding occurs is referred to as the critical count but is not always significant, as a low platelet count is not the only factor which can cause bleeding.



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