ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY
Light micrograph of human lung containing particles of inspired coal dust (anthracosis). Oxygen exchange in the lung occurs at the surface of a fine network of alveoli, a series of empty spaces bounded by brown lines. These boundaries are rich in blood capillaries. Inspired dust particles are removed in the nasal passages and the bronchial tubes. Some may penetrate as far as the alveoli; the black masses are groups of coal dust particles which have been gathered together by phagocytes on the alveolar walls - so-called dust cells. Their action minimises the effect of the dust. Magnification x20 at 35mm size.
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