The Blood Clotting Mechanism

The mechanism of hemostasis can divide into four stages. 1) Constriction of the blood vessel. 2) Formation of a temporary “platelet plug." 3) Activation of the coagulation cascade. 4) Formation of “fibrin plug” or the final clot.

The coagulation cascade is a series of steps in response to bleeding caused by tissue injury, where each step activates the next and ultimately produces a blood clot. The term hemostasis is derived from “hem-”, which means “blood”, and “-stasis”, which means “to stop.” Therefore, hemostasis means to stop bleeding. There are two phases of hemostasis. First, primary hemostasis forms an unstable platelet plug at the site of injury. Then, the coagulation cascade is activated to stabilize the plug, stopping blood flow and allowing increased time to make necessary repairs. This process minimizes blood loss after injuries.

The coagulation cascade involves the activation of a series of clotting factors, which are proteins that are involved in blood clotting. Each clotting factor is an enzyme that speeds up the breakdown of another protein.

The order of the cascade is

 Calcium

Prothrombin

Thromboplastinm

Thrombin  (to create Thrombocytes)

 Fibrinogen

 Fibrin

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