What Are Platelets?

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Platelets are small fragments of cells in the blood that respond to injury by aiding the clotting process. Platelets adhere to the lining of injured blood vessels and create a platform for a fibrin clot to form and cover the wound, according to the American Society of Hematology.

Platelets form in the bone marrow when large cells called megakaryocytes fragment, releasing a thousand platelets per megakaryocyte, according to the University of Oklahoma Health Sciences Center. Surface proteins allow them to bind to blood vessel walls as well as to each other. Platelets also contain proteins that allow them to change shape and extend filaments to attach to a blood vessel wall or to other platelets. When platelets travel along the blood vessel wall and encounter an injury, they change shape to clump with each other onto the fibers of the broken blood vessel and prevent bleeding.

A typical platelet count ranges from 150,000 to 450,000 platelets per microliter of blood, as reported by Johns Hopkins Medicine. When platelet counts fall outside the normal range, disorders develop. Too many platelets result in a condition called thrombocytosis, which can lead to spontaneous clotting and possibly a heart attack or stroke. Too few platelets result in thrombocytopenia, which can lead to frequent bleeding and easy bruising.