PHOTO INSOLITE REALITE / SCIENCE PHOTO LIBRARY PHOTO INSOLITE REALITE / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph (SEM) of the interior surface of a human bronchus, one of the larger elements of the bronchial tree, which conducts air to the alveoli (air sacs) of the lung, where gaseous exchange takes place. The bronchial epithelium is covered with cilia (feathery in appearance) and mucous-secreting cells (not visible in this image), which filter the incoming air of dust particles (the cilia are fine projections, which beat constantly, directing dust particles back towards the trachea). The mucous secreted helps scrub the air of harmful gases such as ozone and sulphur dioxide. Magnification: X 800 at 35mm size.
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