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| Platelets |
(Gk. thrombos-clot, kytos- hollow cell)
Platelets are non-nucleated, round and biconvex. They are the smallest elements of blood measuring about 2.5 to 5 μm in diameter. They are about 2.5 lakhs per cubic mm in blood. Their life span is about 5 to 10 days. Thrombocytes are fragments formed from large cells called megakaryocytes of bone marrow. Formation of platelets is called thrombopoiesis. Increase in platelets is called thrombocytosis, whereas decrease in platelet count is called thrombocytopenia.
Thrombocytes aggregate at the site of injury and form a platelet plug. They release thromboplastin which helps in clotting of blood.