What are platelets and why do I need them?

Platelets are small cells (about one-tenth the size of red blood cells) that help stop bleeding if I am injured. For example, if I have a cut or bruise from playing with my toys, the vessels that carry blood are torn open. Platelets stick to the torn surface of the vessel, clump together and plug up the bleeding. Later, a firm clot forms. The vessel wall then heals at the site of the clot and returns to its normal state. If I do not have sufficient platelets and cut myself, the bleeding may not stop and I may be bleeding inside my body. This can be very dangerous.