TY - CHAP M1 - Book, Section TI - Chapter 439. Disorders of Platelets A1 - Neunert, Cindy E. A1 - Yee, Donald L. A2 - Rudolph, Colin D. A2 - Rudolph, Abraham M. A2 - Lister, George E. A2 - First, Lewis R. A2 - Gershon, Anne A. PY - 2011 T2 - Rudolph's Pediatrics, 22e AB - Platelets arise from megakaryocytic precursors in the bone marrow. Maturation and production is regulated by several general cytokines and the more specific 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.1 Proplatelet extensions form from megakaryocytic cytoplasm; once granule and cytoplasmic organization is complete, platelets are released from the ends of the proplatelet structures. After leaving the marrow, approximately one third of the platelet mass is sequestered in the spleen, while the other two thirds circulate 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 the plasma thrombopoietin level. Platelets have an average diameter of 2.0 to 5.0 mm and typical mean platelet volumes of 6 to 10 femtoliters.1 Their external surface consists of a lipid bilayer containing a variety of structural glycoproteins. The anuclear cytoplasm contains dense granules, which store calcium, serotonin, adenosine diphosphate (ADP), and adenosine triphosphate (ATP), and the more numerous alpha granules, which contain other biologically active proteins including fibrinogen, von Willebrand factor, factor V, and other adhesive molecules. SN - PB - The McGraw-Hill Companies CY - New York, NY Y2 - 2024/03/28 UR - accesspediatrics.mhmedical.com/content.aspx?aid=7040718 ER -