SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY SUSUMU NISHINAGA / SCIENCE PHOTO LIBRARY
Lung lining. Coloured scanning electron micrograph (SEM) of mucus-producing cells (orange, round) and cilia (yellow) lining a bronchus (lung airway). Mucus drops (pale pink, one at upper left and one at lower right) and a piece of dust (pale green, upper right) are also seen. Mucus secreted by the lungs traps bacteria, dust and other particles. Rhythmic movements of the cilia serve to move the mucus and the trapped particles away from the gas-exchanging parts of the lung, and towards the throat, where they can be expelled.
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