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Platelets

Platelets. Size: 1 – 4 Micro meter in diameter Normal Count: 1, 50000 – 300,000 / cu mm or micro liter Live span: 10 days Megakaryocyte 35-160 micron. Platelet membranes contain receptors for Collagen ADP Vessel wall Von Willebrand factor Fibrinogen Glycoprotein Prothrombin.

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Platelets

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  1. Platelets Size: 1 – 4 Micro meter in diameter Normal Count: 1, 50000 – 300,000 / cu mm or micro liter Live span: 10 days Megakaryocyte 35-160 micron

  2. Platelet membranes contain receptors for • Collagen • ADP • Vessel wall Von Willebrand factor • Fibrinogen • Glycoprotein • Prothrombin

  3. Platelets cytoplasm contain • Actin • Myosin • Thrombosthenin • Glycogen • Lysosomes • Fibrin stabilizing factor • Granules • 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.

  4. Regulation of Platelet Production • Thrombopoietin • Erythropoietin • Menstrual cycle • Adrenaline • Injury • Hypoxia • Smoking • Vitamin deficiency

  5. Thrombocytosis Increase no of platelets in the blood Causes. • After acute haemorrhage • Splenectomy • Polycythemia vera

  6. Thrombocytopenia Decreased Number of platelets in the blood Causes. • Idiopathic • Secondary • Pancytopenia • Increased destruction of platelets • Hypersplenism • Leukemia

  7. Hemostasis Arrest of bleeding/ prevention of blood loss when there is vessel injury Involves three steps A. Vascular spasm • Inherent vascular response • Sympathetically induced vasoconstriction • Vasoconstrictor substance e.g Thromboxane A2. B. Formation of platelet plug • Platelet adhesion • Platelet activation • Platelet aggregation. C. Clot formation • Intrinsic system • Extrinsic system • Growth of fibrous tissue in clot

  8. Formation of Platelet Plug

  9. Functions of Platelet Plug • Seals the break in the vessel • Strengthens loose plug –actin and myosin • Reinforce initial vascular spasm—serotonin, epinephrine, thromboxane A2 • Enhances blood coagulation

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