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Sixth lecture

Sixth lecture. HEMOSTASIS. Mechanism of hemostasis:. 1-Vascular spasm 2-Platelet plug formation 3-Formation of blood clot. 4-Repair of the damaged blood vessel. Mechanism of hemostasis:. 1-Vascular spasm: a-Nervous system reflexes which are initiated by pain.

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Sixth lecture

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  1. Sixth lecture

  2. HEMOSTASIS Mechanism of hemostasis: 1-Vascular spasm 2-Platelet plug formation 3-Formation of blood clot. 4-Repair of the damaged blood vessel.

  3. Mechanism of hemostasis: 1-Vascular spasm: a-Nervous system reflexes which are initiated by pain. b-Local myogenic contraction of the injured vessel. c-Release of serotonin a vasoconstrictor. 2-Platelet plug formation: a-Exposed collagen attracts platelets which stick to it and release ADP while their enzymes form thromboxaneA2. b- These substances attract more platelets leading to the formation of a loose plug

  4. Mechanism of hemostasis: 3-Formation of blood clot: a-Through blood coagulation, the temporary platelet plug is stabilized by fibrin threads & is converted to a strong fibrin clot that can seal the wound and maintain hemostasis. b-A few minutes later, clot retraction starts & is completed within 20-60 min. c-A certain contractile protein (retractozyme) pulls the edges of the wound inwards

  5. Mechanism of hemostasis 4-Repair of the damaged blood vessel: The fibroblasts, the vascular smooth muscle & endothelial cells grow and proliferate by the effect of a growth factor released by the platelets as well as macrophages & endothelial cells.

  6. INITIATION OF BLOOD COAGULATION Extrinsic Pathway Intrinsic Pathway Tissue trauma Leakage of Tissue Factor Blood trauma/ contact with collagen Activation of factor XII, IX, VIII Ca+2, factor VII XXa XXa Ca+2 Ca+2 Prothrombin activator Prothrombin activator Ca+2 Prothrombin Thrombin (factor II) Prothrombin Thrombin (factor II) Activation of certain factors (VII, II, X and protein C and S) is essential for coagulation. This activation requires vit K (reduced form)

  7. BLOOD COAGULATION Thrombin Fibrin Monomers Fibrinogen Ca+2, factor XIII Fibrin threads

  8. Platelets • A clot with platelet, fibrin mesh & RBC s

  9. Blood pro-clotting factors Factor I Fibrinogen *vWF is an exception Factor II Prothrombin Factor III Tissue Factor Factor V Cofactor Factor VII With TF Activate X & IX Factor VIII Cofactor Factor IX Christmas - Activates X Factor X Stuart-Prower - Converts prothrombin Factor XI Activates IX Factor XII Hageman - Activates XI Prekallikrein Fletcher - Activates XII HMWKininogen Cofactor

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