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Definition
Platelets
Size: 1 – 4 Micro meter in diameter Normal Count: 1, – 300,000 / cu mm or micro liter Live span: 10 days Platelet membranes contain receptors for Collagen ADP Vessel wall Von Willebrand factor Fibrinogen Glycoprotein
Platelets cytoplasm contain Actin Myosin Thrombasthenin Glycogen Lysosomes Granules I.Dense granules Contains non protein substances e.g. Serotonin, ADP, Ca and other nucleotides. II. Alpha granules: Secrete proteins e.g. Clotting factors, platelet derived growth factor (PDGF), Von Willebrand factor.
Regulation of Platelet Production Thrombopoietin Erythropoietin Adrenaline Injury Hypoxia Smoking
Thrombocytopenia Decreased Number of platelets in the blood Causes. 1.Idiopathic 2.Secondary a.Pancytopenia b.Increased destruction of platelets c.Splenomegaly d.Leukemia
Thrombocytosis Increase no of platelets in the blood Causes. 1.After acute haemorrhage 2.Splenectomy 3.Polycythemia vera
Hemostasis “Arrest of bleeding” is called hemostasis. It involves three steps 1.Vascular spasm a.Inherent vascular response b.Sympathetically induced vasoconstriction 2.Formation of platelet plug a.Platelet adhesion b.Platelet activation c.Platelet aggregation 3.Clot formation a.Intrinsic system b.Extrinsic system
Activated Platelets
Platelet plug Formation
Factors involved in Platelet Function
Whenever the vessel is damaged, the net result is formation of prothrombin activator. Prolthrombin activator is formed in two ways a.The extrinsic pathway b.The intrinsic pathway
Intrinsic Pathway for initiating Clotting Intrinsic pathway
Extrinsic Pathway for initiating Clotting Extrinsic Pathway
Erythrocytes trapped in the fibrin meshwork of a clot (Clot formation)
Roles of Thrombin
Concurrent Platelet Aggregation and Clot Formation
Hemostasis
Factors involved in Clotting
Role of Factor XII
Fibrinolytic system Plasminogen Activator Plasminogen Plasmin Fibrin Fibrin Degradation Products FDPs. Prevent platelet aggregation Inhibit thrombin formation Prevent fibrin polymerization Plasmin also digests factors I,II,V, VIII and XII.
Endogenous factors involved in Fibrinolysis and Anticoagulation
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