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Physiology of Blood Platelets • • • • Small granulated non-nucleated bodies 2-4 micron in diameter Life span….. 8 days Count…300,000/mm3 Hemostasis It is a prevention of blood loss after injury Mechanism 1. Constriction of the blood vessel . local myogenic contraction, nervous reflex & local factors ( serotonin, ADP ,thromboxane A2) 2. Formation of platelet plug 3. Conversion of platelet plug to a definitive clot by fibrin threads ( blood clot) 4. Dissolution of the clot by plasmin after tissue repair 2- Platelet plug formation Platelet reactions 1- Platelet adhesion ( to subendothelial collagenneeds von-Willebrand factor) 2- Platelet activation ( swell& change the shape) 3- Platelet release reaction ( Ca2+ ,coagualtion factors, serotonin, thromboxane A2........ 4- Platelet aggregation ( platelet plug) 5- Platelet procoagulant activity ( activation of coagulation factors) 6- Platelet fusion ( fusion of aggregated platelets) 3- Formation of blood clot (Mechanism of blood coagulation) Intrinsic pathway subendothelial collagen Extrinsic pathway tissue injury FXII Tissue thromboplastin FIII FVII FXI FIX FVIII, Ca,Pl Pl,Ca2+ active FX FX Pl, FV, Ca2+ Prothrombin thrombin Fibrinogen Fibrin Coagulation factors • Plasma proteins synthesized by the liver • Most are known by capital Roman numerals • Inactive serine protease enzymes which when activated lead to activation of other factors in a cascade effect 4- Dissolution of the clot by plasmin after tissue repair Plasmin ( fibrinolysin) • Plasmin is formed from inactive plasminogen by the action of tissue plasminogen activator TPA & thrombin • Plasmin lyses fibrin & fibrinogen into fibrinogen degradation products Anticlotting mechanisms General limiting reactions…smooth endothelium, rapid blood flow, heparin, liver Specific limiting reaction • Prostacyclin # thromboxane A2 • Antithrombin III …… inhibits F IX, X, XI, XII • Protein C & protein S ….inhibit F V & VIII • Fibrinolytic system ( plasmin)……lyses of fibrin Anticoagulants ( heparin , dicumarol ) In vitro anticoagulants……precipitation of Ca 2+ ,silicon coated tubes & heparin In vivo anticoagulants …….. Heparin & dicumarol Anticoagulant origin heparin dicumarol Mast cells & basophiles Plant Mode of action Facilitates ant thrombin III Inhibit vitamin K Site of action In vivo & in vitro Only in vivo Onset rapid slow Duration short long Administration Iv, im Orally antidote Protamin sulphat Vitamin K Abnormalities of hemostasis Thrombocytopenic purpura Decreased platelet count Subcutaneous hemorrhage Plonged bleeding time Vitamin k deficiency vit K is important for formation of factors II,VII, ,IX, X in the liver It is a fat soluble vitamin & is formed by intestinal flora Its absorption is decreased in obstruction of bile duct Hemophilia Congenital sex-linked disease transmitted by females to males Characterized by sever bleeding after trauma It is due to absence of factor VIII or IX or XI White blood cells 4000-11000 Granulocytes Neutrophils----50-70% ingest & kill bacteria Agranulocytes Lymphocytes 20-40% immunity Esinophils 1-4 % parasites & allergy Monocytes 2-8% tissue macrophage Basophils 0.5% histamine & heparin Immunity Specific Non specific •Doesn't’ depend on antigen type •Mechanical & chemical barriers •Cells phagocytes & macrophages natural killer cells •Complement •interferon Humoral Antibody- mediated Bacteria B-lymphocytes (antibodies) Antigen specific lymphocytes Cellular Cell-mediated Virus Antigen presenting cells T-lymphocytes
