PLATELET


Meaning of PLATELET in English

also called Thrombocyte, small, colourless, nonnucleated, usually round body that is very important in the formation of blood clots and is 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. The platelet is metabolically more active than the red blood cell and has a variety of functions. Platelets play an important and not fully understood role in the formation of the blood clot by coagulating to occlude a cut blood vessel and provide a surface on which strands of fibrin (q.v.) form an organized clot, by contracting to pull the fibrin strands together to make the clot firm and permanent, and, perhaps most important, by providing or mediating a series of coagulation factors necessary to the formation of the clot. Platelets also store and transport several chemicals, including serotonin, epinephrine, and histamine (the importance of which in this capacity is unknown), and they phagocytose (absorb) foreign bodies, including viruses, as well. At birth the number of platelets is low, but by three months of age the adult level is reached. The number of platelets rises following trauma or asphyxiation, at high altitudes, after exercise, and in cold weather; the number may be temporarily lowered by menstruation in women. Certain chemicals may prolong the life of platelets; smoking is believed to shorten their life spans. Platelets are produced in the bone marrow and stored in the spleen. Some evidence suggests they may also be produced or stored in the lungs, where megakaryocytes are frequently found. Individuals may develop antibodies to platelets following repeated platelet or whole-blood transfusion.

Britannica English vocabulary.      Английский словарь Британика.