Caption

Cilia in the trachea. Coloured scanning electron micrograph (SEM) of cilia on the epithelium lining the trachea (windpipe) of an 11 week old foetus. During the breathing process (after this foetus is born) the hair-like cilia will beat rhythmically, filtering particles in the air and sweeping dust and other foreign material up towards the larynx and mouth. The epithelium also produces mucus which traps large dust particles and helps to remove gaseous pollutants from the inhaled air. Magnification: unknown.