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.
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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.