Practical 3 Clotting-time_organized part 1.pdf

Haemostasis 3-Firm platelet plug (clot) formation: - Clot (coagulation) is formed by conversion of soluble fibrinogen into insoluble fibrin network with blood cells (as platelets) in its meshes, this through 4 stages, via clotting factors: - Clotting factors (e.g. fibrinogen, prothrombin) present in...

Haemostasis 3-Firm platelet plug (clot) formation: - Clot (coagulation) is formed by conversion of soluble fibrinogen into insoluble fibrin network with blood cells (as platelets) in its meshes, this through 4 stages, via clotting factors: - Clotting factors (e.g. fibrinogen, prothrombin) present in blood in as inactive enzymes (then activated by cascade of reactions). - Clotting factors are 12 factors ( from I to XIII), but no VI factor. - All clotting factors are synthesized in liver except factor III (tissue factor) and factor IV (Ca+2). - All the clotting factors circulate in the blood except factor III (tissue factor is released from damaged tissues Coagulation system Normal coagulation system requires coagulation factors; 3-Firm platelet plug (clot) formation: Mechanisms of blood coagulation (clotting):  Blood coagulation can occur through the following four stages (cascade reactions or theory): 1- Formation of prothrombin activator through intrinsic or extrinsic clotting mechanism. 2-Conversion (activation) of prothrombin (factor II) into thrombin (factor IIa) by prothrombin activator. 3-Conversion of soluble fibrinogen into soluble fibrin by thrombin. 4-Conversion of soluble fibrin into insoluble fibrin , 3-Firm platelet plug (clot) formation: Mechanisms of blood coagulation (clotting): 2-Stage II (conversion of prothrombin into thrombin): Prothrombin Thrombin 3-Stage III (conversion of fibrinogen into fibrin): Fibrinogen Soluble fibrin. 4-Stage IV (stabilization of fibrin): Soluble fibrin Factor XIII & Ca + + ⎯⎯ ⎯ ⎯ ⎯ ⎯ ⎯→ Insoluble fibrin.