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mast cell[′mast ‚sel]
(also called mastocyte or labrocyte), a reticular connective tissue cell in animals and man. The number of mast cells depends on the species and on the functional state of the connective tissue. The mast cell contains metachromatic cytoplasmic granules; the size and number of granules depend on the species and on the maturity and functional state of the cell. Mast cells contain a number of physiologically active substances, notably heparin, histamine, and serotonin. Consequently, it is believed that the mast cell plays a role in anaphylaxis, inflammation, and blood clotting. Mast cells rarely divide by mitosis. The principles of their origin and reproduction remain obscure.