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Showing posts from September, 2012

Platelets / Thrombocytes

Introduction: Platelets are also called as thrombocytes. Size: they are very small discs with diameter varying from 1 to 4 micrometers. The normal concentration of platelets in the blood is between 150,000 and 450,000 per microliter. Formation: They are formed in the bone marrow from megakaryocytes. The latter are extremely large cells in the marrow and they fragment into the minute platelets either in the bone marrow or soon after entering the blood. Destruction: The platelet has a half-life in the blood of 8 to 12 days. Then it is eliminated from the circulation mainly by the tissue macrophage system. More than one half of the platelets are removed by macrophages in the spleen, where the blood passes through a latticework of tight trabeculae. Platelets do not have nuclei and cannot reproduce. Yet, they have many functional characteristics of whole cells. 1) Actin and myosin molecules are present in their cytoplasm. They are contractile proteins similar to those found in