Physiology of Blood

Platelets Small granulated non-nucleated bodies 2-4 micron in diameter Life span….. 8 days Count…300,000/mm 3

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 collagen- needs von-Willebrand factor) 2- Platelet activation ( swell& change the shape) 3- Platelet release reaction ( Ca 2+,coagualtion factors, serotonin, thromboxane A 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 FXI FIX Tissue thromboplastin FIII FVII F X active FX Prothrombin thrombin Fibrinogen Fibrin FVIII, Ca,Pl Pl, FV, Ca 2+ Pl,Ca 2+

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 A 2 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 dicumarolheparin PlantMast cells & basophilesorigin Inhibit vitamin KFacilitates ant thrombin IIIMode of action Only in vivoIn vivo & in vitroSite of action slowrapidOnset longshortDuration Orally Vitamin K Iv, im Protamin sulphat Administration antidote

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 Granulocytes Neutrophils % ingest & kill bacteria Esinophils 1-4 % parasites & allergy Basophils 0.5% histamine & heparin Agranulocytes Lymphocytes 20-40% immunity Monocytes 2-8% tissue macrophage

Immunity Non specific Doesn't’ depend on antigen type Mechanical & chemical barriers Cells phagocytes & macrophages natural killer cells Complement interferon Specific Antigen specific lymphocytes Humoral Antibody- mediated Bacteria B-lymphocytes (antibodies) Cellular Cell-mediated Virus Antigen presenting cells T-lymphocytes