Define blood clotting and describe the mechanism of blood clotting.

Blood clotting : It is the natural device to check bleeding. The clot is a reddish brown scum which is formed at the site of a cut or an injury over a period of time. The clot consists mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.
An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation. Certain
factors released by the tissues at the site of injury also can initiate coagulation. Calcium ions play a very important role in clotting.

i. The fibrins are formed by the conversion of inactive fibrinogens in the plasma by the action of the enzyme thrombin.
ii. Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. This reaction is brought about by the enzyme thrombokinase. TThe clot is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive
state.