False-colour scanning electron micrograph (SEM) of the internal lining, or epithelium, of the bronchial passages in the human lung. Clumps of fine hairs, called cilia, protrude from the tops of specialised epithelial cells (reddish-brown). The micrograph also shows the round goblet cells (yellow) whose function is to release mucus onto the surface of the epithelium. Rhythmic movements of the cilia serve to move bacteria & other particles away from the gas-exchanging parts of the lung & towards the throat where they can be swallowed or coughed up. Magnification: x2,000 at 6x7cm, x1,000 at 35mm size.