(N/A) Blood coagulation or clotting is a protective mechanism that occurs in response to an injury to prevent excessive blood loss.
The clot or coagulum is primarily composed of a network of thread-like proteins called $Fibrins$,in which dead and damaged formed elements of blood (cells) are trapped.
$Fibrins$ are formed by the conversion of inactive $Fibrinogens$ present in the plasma by the enzyme $Thrombin$.
$Thrombins$ are in turn formed from inactive $Prothrombin$ present in the plasma with the help of an enzyme complex called $Thrombokinase$.
The reaction sequence is as follows:
$Prothrombin \xrightarrow{Thrombokinase} Thrombin$
$Fibrinogen \xrightarrow{Thrombin} Fibrin$
This process involves a cascade of linked enzymatic reactions involving various clotting factors present in the plasma in an inactive state.
An injury or trauma stimulates the platelets in the blood to release certain factors which activate the coagulation mechanism.
$Calcium$ ions $(Ca^{2+})$ play a very important role in the clotting process.