Platelets

Platelets (thrombocytes) are normal constituents of blood that are essential for normal hemostasis. They are fragments of megakaryocyte cytoplasm that arise in the bone marrow at a rate of ~10¹¹ per day to maintain a normal concentration of 2 to 3 x 10⁸/mL. Platelets localize to sites of vascular injury to form a plug, which slows or stops bleeding.