Clotting is a natural phenomenon that checks excessive loss of blood in case of injury. Clotting takes place whenever the tissue is injured. There are three types of cells in our blood-red blood ceels, white blood cells and platelets. It is these platelets that help in forming clots to stop bleeding.
The platelets gather at the site of the injured cell and prevent the red blood vessels from flowing out. They from a plug across the opening and release chemicals that convert liquid blood protein fibrinogen into insoluble fibrin. Fibrin forms a mesh of thread like fivers that trap platelets and other blood cells, thereby forming a clot.