- An irregular, disc-shaped element in the blood that assists in blood clotting. During normal blood clotting, the platelets clump together (aggregate). Although platelets are often classed as blood cells, they are actually fragments of large bone marrow cells called megakaryocytes.
* * *An irregularly shaped disklike cytoplasmic fragment of a megakaryocyte that is shed in the marrow sinus and subsequently found in the peripheral blood, where it functions in clotting. A p. contains granules in the central part (granulomere) and, peripherally, clear protoplasm (hyalomere), but no definite nucleus; is about one-third to one-half the size of an erythrocyte; and contains no hemoglobin. SYN: Bizzozero corpuscle, blood disk, elementary bodies (2), elementary particle (1), third corpuscle, thrombocyte, thromboplastid (1), Zimmermann corpuscle. [see plate]
* * *plate·let 'plāt-lət n a minute colorless anucleate disklike body of mammalian blood that is derived from fragments of megakaryocyte cytoplasm, that is released from the bone marrow into the blood, and that assists in blood clotting by adhering to other platelets and to damaged epithelium called also blood platelet, thrombocyte
* * *n.a disc-shaped cell structure, 1-2 µm in diameter, that is present in the blood. With Romanowsky stains platelets appear as fragments of pale-blue cytoplasm with a few red granules. They have several functions, all relating to the arrest of bleeding (see blood coagulation). There are normally 150-400 x 109 platelets per litre of blood. See also thrombopoiesis.
* * *plate·let (plātґlət) a disk-shaped structure, 2 to 4 μm in diameter, found in the blood of all mammals and chiefly known for its role in blood coagulation; platelets, which are formed in the megakaryocyte and released from its cytoplasm in clusters, lack a nucleus and DNA but contain active enzymes and mitochondria. See also under factor, and see thrombocytic series, under series. Called also blood p. and thrombocyte.
Medical dictionary. 2011.