Blood Coagulation
Definition
When blood is shed or collected in a container it loses its fluidity and becomes a jelly like mass after a few minutes. This is called clotting or the coagulation of blood.
Blood-Clot
The clot is a mesh of thin fibrils,these fibrils consist of fibrin. Fibrin is formed from Fibrinogen.Coagulation of blood occurs through a series of reactions due to activation of group substances. These substances are necessary for clotting, called clotting factors. 13 clotting factors are identified in our body.
Factor I Fibrinogen
Factor II Prothrombin
Factor III Thromboplastin (Tissue factor)
Factor IV Calcium
Factor V Labile factor (Proaccelerin or accelerator globulin)
Factor VI Presence has not been proved
Factor VII Stable factor
Factor VIII Antihemophilic factor (Antihemophilic globulin)
Factor IX Christmas factor
Factor X Stuart-Prower factor
Factor XI Plasma thromboplastin antecedent
Factor XII Hageman factor (Contact factor)
Factor XIII Fibrin-stabilizing factor (Fibrinase).
Sequence of clotting mechanism:
In general blood clotting occurs in three stages;
1. Formation of prothrombin factor.
2. Conversion of prothrombin into thrombin.
3. Conversion of fibrinogen into fibrin.
During the process of clotting the factors which are in inactive form are converted into their active form. There is enzymatic action to produce sequence of reations.
Extrinsic Pathway & Intrinsic Pathway
Factor XII (XII) (Hageman Factor) is a single chain (Mr=78,000) glycoprotein zymogen that circulates in plasma at a concentration of 40 µg/ml. Reciprical activation of XII to the active serine protease factor XIIa (XIIa) by kallikrein is central to initiation of the intrinsic coagulation p factor xiii
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