STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY STEVE GSCHMEISSNER / SCIENCE PHOTO LIBRARY
Mast cell. Coloured transmission electron micrograph (TEM) of a section through a mast cell, a type of leucocyte (white blood cell). The nucleus (pink & dark blue) is surrounded by cytoplasm (light brown) containing granules (black). The mast cell is in a matrix of connective tissue (light brown fibres, seen at upper left for example). Histamine, heparin and serotonin are stored in the granules until an immune response triggers them to be released. This results in blood vessel dilation and increased capillary permeability, helping other immune cells to find and then destroy the foreign body causing the response. Magnification unknown.
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