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Noun, pl. platelets

1. Colourless, nonnucleated blood component that is important in the formation of blood clots (coagulation). Platelets are found only in the blood of mammals. Platelets are formed when cytoplasmic fragments of megakaryocytes, which are very large cells in the bone marrow, pinch off into the circulation as they age. They are stored in the spleen. Some evidence suggests platelets may also be produced or stored in the lungs, where megakaryocytes are frequently found. (

2. Small, disk shaped clear cell fragments (i.e. cells that do not have a nucleus), 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days. Platelets are a natural source of growth factors. They circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots. (

3. A small colorless disk-shaped particle found in the blood of mammals, which plays an important role in the formation of blood clots. (

4. A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. (

5. A minute flattened body (as of ice or a mineral); especially : a minute colorless disklike body of mammalian blood that assists in blood clotting by adhering to other platelets and to damaged epithelium. (

Syn: thrombocytes

Word origin: From Medieval Latin plata “plate, piece of metal,” perhaps via Vulgar Latin *plattus, formed on model of Greek platys “flat, broad” + diminutive suffix -let.

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