Blood coagulation or clotting is a mechanism to prevent excessive loss of blood. The clot or coagulam is a dark reddish brown scum formed at the site of an injury. It is formed mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. Fibrins are formed by the conversion of inactive fibrinogens present in the plasma by the enzyme thrombin.
Erythrocytes or red blood cells are the most abundant of all the cells in blood. They have a red coloured, iron containing haemoglobin protein complex. RBCs have an average life span of 120 days after which they are destroyed in the spleen which is known as graveyard of RBCs.