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Platelets/ megakaryocytes Normal value: 1.5-4 lakh cells/cumm of blood. Size : 1.5-3 microns Life span : 8-12 days Destruction by spleen Structure of platelets • • • • • Small anucleate cells Highly developed cytoskeletal system Granulated Extensive microtubules and microfilaments Frequently change shape with very long thin processes extending out called filopodia. Cell membrane • Exterior glycocalyx coat • Negative charge on the surface due to sialic acid residues along with glycoproteins prevent adherence to each other and endothelium. • Open canalicular systems • Dense tubular systems • Platelet granules - alpha granules - dense granules Variations : Thrombocytosis. Splenectomy. After trauma: surgery ,injury ,child birth. Adminstration of epinephrine. Stress . Thrombocytopenia: Bone marrow depression. Hypersplenism Viral infection Eg: Dengue fever. Drug hypersensitivity Functions of platelets: Hemostasis: Temporary platelet plug. Blood coagulation: Release clotting platelet Factor 4, V, XI, XIII PL ,HMWK. Clot retraction Thrombolysis Phagocytic function: Storage and transport function: Vasoconstriction Wound healing and vascular growth : Platelet derived growth factor Platelet disorder: A. Thrombocytopenia: Reduction in the platelet count secondary to some other cause. B . Idiopathic thrombocytopenia: Reduction in the number of platelets due to unknown cause. C. Thromboasthenia : Defective platelet function.