The result is that blood does not clot the way it should. Blood is carried throughout the body within a network of blood vessels. When tissues are injured, damage to a blood vessel may result in leakage of blood through holes in the vessel wall. The vessels can break near the surface, as in a cut. Or they can break deep inside the body, making a bruise or an internal hemorrhage.
Platelets are small cells circulating in the blood.
There are 150 to 400 billion platelets in a normal litre of blood. The platelets play an important role in stopping bleeding and beginning the repair of injured blood vessels. When a blood vessel is damaged, there are four stages in the normal formation of a clot. See Figure 1. The blood vessels constrict to slow the flow of blood to the injured area.