Platelets are made in the bone marrow, shedding from mature megakaryocytes in response to thrombopoetin. Also known as thrombocytes, platelets play a role in hemostasis, that to prevent excessive blood loss. Each of these changes can potentially be used as a antegin of platelet activation. Platelet surface CD antigens before activation, like as CD41, CD42a, CD42b, and CD61. And there are CD anrigens as CD31, CD62P and CD63 which appeared on the platelet surface during activation.