Lining of the trachea (windpipe), coloured scanning electron micrograph (SEM). The tracheal lining contains mucus secreting goblet cells (blue) and ciliated epithelial cells (green). The goblet cells secrete a viscous mucus which is able to trap particles inhaled in air whilst breathing. The movement of the long, hair-like cilia on the epithelial cells moves the mucus and any other foreign particles upwards and out of the respiratory tract keeping the lungs and airways free. Magnification: x1000 when printed at 10cm wide.