in Body Fluids and Circulation (Cardiovascular System, Circulatory system) by

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The Coagulation of Blood after any injury (open wound) is a formation of the clot or plug at that site, to arrest the bleeding. Following is the explanation or the steps of Blood coagulation.

There are three processes involved in the coagulation of Blood:

The hemostasis primarily involves the two processes:

1. Vasoconstriction:

It is the process by which the Vessels gets contracted to arrest the bleeding. It is the first process, which starts just after the injury. This process reduces the blood flow at the site of injury.

2. Plug Formation:

The Plug is formed by the aggregation of the platelets at the site of injury to stop the bleeding. Further the platelets start next process of clot formation by the fibrin formation. It is the secondary hemostasis process.

Secondary Hemostasis: It includes the process of clot formation by the fibrin

3. Clot Formation:

In order to arrest the Bleeding the Platelets alone are not sufficient. The Formation of Clot is necessary to stop the bleeding. For the clot to occur the different substances play the role, they are called as the clotting factors. Roman numbers denotes them. In total there are 13 clotting factors. The clotting cascade is the process in which the clotting factors activate each other for the clot formation. The soluble plasma protein is formed at the end of the clotting cascade, which is further cleaved into the fibrin. The fibrin is an insoluble plasma protein, which sticks together and thus forming a clot at the site of injury.

There are two separate pathways involved in the clotting cascade; they are the intrinsic pathway and the extrinsic pathway.

The Intrinsic Pathway: The activation of the intrinsic pathway occurs by the internal trauma in the vascular system. It is activated by the expose endothelium, collagen or the chemicals, and by the platelets. It involves Factor XII (Hageman factor), XI (Plasma thromboplastin antecedent), IX (Plasma thromboplastin component), VIII (Antihemophilic factor {AHF}).

The Extrinsic Pathway: The activation of the extrinsic pathway occurs by the external trauma, which cause the blood to flow out of the vascular system. There is involvement of Factor VII (Serum prothrombin conversion accelerator; proconvertin) in this pathway. It is quicker pathway compared to the intrinsic pathway.

The Common Pathway for the Clot Formation: Finally both the intrinsic and the extrinsic pathway connect and complete the formation of the clot. The common pathway includes Factor I (Fibrinogen), II (Prothrombin), V (Proaccelerin; Labile factor), and X (Stuart-Power factor).

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