Blood Clotting - Coagulation of blood at wound to prevent excess loss of blood.
Clotting occurs in a series of steps as follows -
1. At the site of wound, platelets release an enzyme thrombokinase or thromboplastin (also called Factor 'X' or Stuart factor)
2. Thrombokinase along with calcium ion present in blood plasma, converts inactive Prothrombin into active Thrombin.
3. Thrombin in presence of calcium ions reacts with Fibrinogen (a soluble protein present in blood plasma) and convert it in to insoluble Fibrin.
4. Fibrin in the form of fine threads make a network (mesh) at wound.
5. Blood cells are trapped in the network of Fibrin & then the network shrinks and squeezes out rest of the plasma in the form of a clear liquid called serum.
6. The solid mass which left behind is called clot or Thrombus.