CNRI / SCIENCE PHOTO LIBRARY CNRI / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph (SEM) of the ciliated epithelium of the human trachea (windpipe). The epithelium is composed of two types of cell; ciliated cells with long, grass- like projections (orange) and mucous-secreting goblet cells (purple), which are covered in short microvilli. The mucous secreted by the goblet cells serves to trap large dust particles and also to scrub inhaled air of gaseous pollutants such as ozone & sulphur dioxide. A rhythmic beating of the numerous cilia also acts as a filter to particles suspended in the incoming air, sweeping dust and other foreign material back towards the larynx. Magnification: x700 at 6x7cm, x350 at 35mm size.
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