Blood Clotting
DEFINITION
Coagulation or clotting is defined as the process in which blood losses its fluid and becomes a jelly like mass few minutes after it is shed out ot collected in a container.
FACTORS INVOLVED IN BLOOD CLOTTING
Coagulation of blood occurs through a series of reactions due to the activation of a group of substances necessary for clotting are called clotting factors.
Thirteen clotting factors are identified.
1. Factor 1: Fibrinogen
2. Factor-II: Prothrombin
3. Factor III:Thromboplastin (Tissue Factor)
4. Factor-IV: Calcium
5. Factor-V: Labile Factor
6. Factor VI: Presence has not been proved
7. Factor VII: Stable factor
8. Factor VIII: Antihemophillic factor (Antihemophillic globulin)
9. Factor-IX:Christmas Factor
10. Factor-X: Stuart Prower factor
11. Factor-XI: Plasma Thromboplastin Antecedent
12. Factor-XII: Hageman factor (Contact factor)
13. Factor-XIII: Fibrin stabilizing Factor (Fibrinase)
STEPS OF BLOOD CLOTTING
In general blood clotting occurs in three stages.
1) Formation of Prothrombin activator
2) Conversion of prothrombin into thrombin
3) Conversion of fibrinogen into fibrin
STAGE 1: FORMATION OF PROTHROMBIN ACTIVATOR
Blood clotting commences with the formation of a substance called prothrombin activator, which converts prothrombin into thrombin.
Its formation is initiated by substances either within the blood or outside the blood.
Thus, formation of prothrombin activator occurs through two pathways:
1. Intrinsic Pathway
2. Extrinsic Pathway
STAGE 2: CONVERSION OF PROTHROMBIN INTO THROMBIN
Blood clot is all about thrombin formation. Once thrombin is formed definitely it leads to clot formation.
Prothrombin activator that is formed in intrinsic and extrinsic pathways converts prothrombin into thrombin. In the presence of calcium (factor IV). Once formed thrombin initiates the formation of more thrombin molecules.
The initially formed thrombin activates factor V.
Factor V in turn accelerates formation of both extrinsic and intrinsic prothrombin activator, which converts prothrombin into thrombin. The effect of thrombin is called positive feedback effect.
STAGE-3: FIBRINOGEN INTO FIBRIN
Sequence of events in stage 3 are as follows.
1. Thrombin converts inactive fibrinogen into activated fibrinogen .
The activatedfibrinogen is called fibrin monomer.
2. Fibrin monomer polymerizes with other monomer molecule and form loosely arranged strands of fibrin.
3. Later these loose strands are modified into dense and tight fibrin threads by fibrin stabilizing factor (Factor VIII) in the presence of calcium ions.
4. All the tight fibrin threads are aggregated to form a meshwork of stable clot.
By : ummedsaini_
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