Trachea. Coloured scanning electron micrograph (SEM) of the lining of the trachea (windpipe). The trachea links the larynx (voice box) to the lungs. Its lining contains mucus-secreting goblet cells (brown) and epithelial cells bearing hair-like cilia (red). The mucus serves to trap tiny particles in inhaled air, whilst the movement of the cilia moves the mucus and foreign particles upwards out of the respiratory tract, helping to keep the lungs and airways free. Magnification: x670 at 6x7cm size.