Platelets (thrombocytes).

Platelets are one of the four main components of blood, along with red blood cells (RBCs), white blood cells (WBCs), and plasma. Platelets are also called thrombocytes (THROM-buh-sites). Platelets are cell-like structures primarily responsible for clotting and preventing blood loss when blood vessels become damaged due to injury. An abnormally high number of platelets in the blood can place a person at risk for clots, while an abnormally low number can increase a person's bleeding risk.