Calcium salts, cell injury which liberates thrombokinase, (thromboplastin) thrombin and fibrin.
Prothrombin + Ca + thrombokinase → Thrombin.
Thrombin + fibrinogen → Fibrin Fibrin + bloodcells → Clot (Fibrin clot)
The clotting consists 3 phases.
Stage I: Thromboplastin or thrombokinase is liberated from injured tissue or shed blood.
Stage II: The thromboplastin in the presence of ionic calcium acts on prothrombin, a protein present in the blood plasma and coverts it to thrombin.
Stage III: The thrombin in turn acts on fibrinogen, the soluble protein present in plasma and converts it to fibrin. It is insoluble and precipitates as a net work of elongated thread like fibres enmeshing cellular and liquid components in the mesh work and giving it a solid appearance. Subsequently the fibres shrink an the mesh becomes closely knit. It holds the cellular elements, but exuding out the liquid. The liquid is the serum.
