The plug is composed of platelets and special plasma proteins called fibrin. The platelets pug is enmeshed in a network of insoluble fibrin molecules.
The aggregation of platelets and formation of fibrin both require the enzyme called thrombin. The clotting process also requires calcium ions, and about a dozen other protein clotting factors found in plasma.
When blood vessels are cut or damaged, the loss of blood has to be stopped before shock and possible death occur. This is achieved by solidification of blood, a process called coagulation or clotting.
