The clotting or coagulation of blood involves a series of chemical reactions that culminate in the formation of insoluble fibrin threads from the soluble plasma protein, fibrinogen. The process of coagulation involves two vital steps:
Conversion of prothrombin to thrombin.
Conversion of fibrinogen to fibrin by thrombin.
Injured tissue release thromboplastin and blood platelets disintegrate to release platelet factor-3, both of which combine with calcium ions to form prothrombinase. Prothrombinase inactivates heparin and catalyses the formation of active thrombin from inactive prothrombin. Thrombin acts as an enzyme to convert fibrinogen to fibrin, which combines with blood cells to form the clot.
