Blood platelets or thrombocytes are the smallest cells in the blood; they are even smaller than red blood cells. Platelets play an important role in the coagulation of the blood by sticking to the surrounding tissue or to each other when a blood vessel is injured so as to close the wound and stop the bleeding.

Red blood cells have a relatively long lifespan of approx. 150 days, some lymphocytes likewise live for several months; other white blood cells such as granulocytes only live for a few days.