Virtual Cath Lab Platelets Platelets are the smallest of the formed elements of the blood. Every cubic millimeter of blood contains about 250 million platelets. There are about a trillion platelets in the blood of an average adult.
Platelets are fragments of the giant bone-marrow cells called megakaryocytes.
When a megakaryocyte matures, its cytoplasm breaks up, forming several thousand platelets. However, they contain only about one-thirteenth the volume of a red cell. When released into the blood, they circulate and die in about ten days. The primary function of platelets is that of forming blood clots. This causes the shrinkage of a fresh blood clot after it stands for a few minutes.