Lung lining. Coloured scanning electron micrograph (SEM) of the epithelium lining a terminal bronchiole (lung airway). The epithelium consists of ciliated (hair-covered) cells (yellow), and non-ciliated cells (pink) that secrete mucus. Rhythmic movements of the cilia move mucus and trapped particles away from the gas-exchanging parts of the lung, and towards the throat, where they can be expelled by coughing, or swallowed. Magnification: x2,300 when printed at 10 centimetres wide.