TY - CHAP M1 - Book, Section TI - Disorders of Platelets A1 - Sartain, Sarah E. A1 - Despotovic, Jenny M. A2 - Kline, Mark W. PY - 2018 T2 - Rudolph's Pediatrics, 23e AB - Platelets, like other blood cells, arise from precursors in the bone marrow. Platelet maturation and production from marrow precursors, known as megakaryocytes, is highly regulated by the platelet growth factor, thrombopoietin. Platelet production occurs through the specialized process of endomitosis, by which DNA replicates without cell division, resulting in the polyploid nuclei characteristic of megakaryocytes. Proplatelet extensions form from megakaryocytic cytoplasm; once granule and cytoplasmic organization is complete, platelets are released from the ends of the proplatelets. After leaving the bone marrow, approximately one-third of the platelet mass is sequestered in the spleen, while the remainder circulate in the blood with a life span of 7 to 10 days. Thrombopoiesis is balanced by platelet senescence and consumption to maintain a normal blood platelet count (150,000–400,000/mm3) via plasma thrombopoietin. Platelets have an average diameter of 2.0 to 5.0 µm and typical mean volume of 6 to 10 fL. The platelet external surface consists of a lipid bilayer containing a variety of structural glycoproteins. The anuclear cytoplasm contains abundant alpha granules that contain biologically active proteins including fibrinogen, von Willebrand factor, factor V, and other adhesive molecules. Dense granules are a less abundant but important component of the cytoplasm, and they store and secrete calcium, serotonin, adenosine diphosphate (ADP), and adenosine triphosphate (ATP). SN - PB - McGraw-Hill Education CY - New York, NY Y2 - 2024/10/13 UR - accesspediatrics.mhmedical.com/content.aspx?aid=1182910388 ER -