Platelets( Thrombocytes血小板 Platelets are small, granulated bodies that aggregate at sites of vascular injury they lack nuclei and are 24 um in diameter There are about 300,000/ul of circulating blood and they normally have a half-life of about 4 days The megakaryocytes, giant cells in the bone marrow, form platelets by pinching off bits of cytoplasm and extruding them into the circulation Between 60 and 75% of the platelets that have been extruded from the bone marrow are in the circulating blood and the remainder are mostly in the spleen Splenectomy causes an increase in the platelet coun 〔 thrombocytosisPlatelets (Thrombocytes) 血小板  Platelets are small, granulated bodies that aggregate at sites of vascular injury  They lack nuclei and are 2–4 μm in diameter  There are about 300,000/μL of circulating blood, and they normally have a half-life of about 4 days  The megakaryocytes, giant cells in the bone marrow, form platelets by pinching off bits of cytoplasm and extruding them into the circulation  Between 60 and 75% of the platelets that have been extruded from the bone marrow are in the circulating blood, and the remainder are mostly in the spleen  Splenectomy causes an increase in the platelet count (thrombocytosis)