Trachea epithelium. Coloured light micrograph of a section through the wall of the human trachea (windpipe) showing ciliated epithelium. Cells of the epithelium are seen here, with the surface layer of cells containing hair-like cilia (at top) which project into the air space of the trachea. The nuclei of these cells are red. Goblet cells (orange) secrete mucus which traps dust particles and other air pollutants, while the beating cilia sweep the foreign matter and mucus back up towards the larynx and out of the lungs. Connective tissue containing bands of fibro-elastic tissue (lower left and right) is found below the epithelium. Magnification: x800 at 6x7cm size. Magnification: x600 at 6x4.5cm size