Mucus The respiratory tract, from nasal cavities to the smallest bronchi, is lined by a layer of sticky mucus, secreted by the epithelium assisted by small ducted glands. Particles which hit the side wall of the tract are trapped in this mucus. This is encouraged by: (a) the air stream changing direction, as it repeatedly does in a continually dividing tube. (b) random (Brownian) movement of small particles suspended in the airstream. The first of these works particularly well on more massive particles, the second on smaller bits Cilia Once the particles have been sidelined by the mucus they have to be removed, as indeed does the mucous. This is carried out by cilia on the epithelial cells which move the mucous continually up or down the tract towards the nose and mouth. (Those in the nose beat downwards, those in the trachea and below upwards). The mucus and its trapped particles are and bacteria are then swallowed, taking them to the sterilising vat of the stomach.
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This note was uploaded on 11/08/2011 for the course BIOLOGY BSC1086L taught by Professor Leostouder during the Fall '10 term at Broward College.