Normal Mechanism of Blood Coagulation

FIGURE 25-1 Mechanism of blood coagulation. Factors involved in clot formation are shown above the dashed line factors involved in clot breakdown are shown below the dashed line. See text 

Clot formation involves the activation of various clotting factors circulating in the bloodstream.108,135 The clotting factors are proteolytic enzymes synthesized in the liver that remain inactive until there is some injury to a blood vessel. Blood vessel damage begins a cascade effect, whereby one of the clotting factors is activated, which leads to the next factor s activation, and so 

Both the intrinsic and extrinsic systems ultimately lead to the conversion of prothrombin to thrombin.92 Thrombin is an enzyme that quickly converts the inactive fibrinogen molecule to fibrin. Individual strands of fibrin bind together to form a meshlike structure, which ultimately forms the framework for the blood clot. Other cellular components, especially platelets, help reinforce the clot by sticking to the fibrin mesh. 

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