Nasal lining. Transmission electron micrograph (TEM) of a section through cilia (red) covering the epithelial lining of the nasopharyx, the part of the throat behind the nasal cavity. Cilia are microscopic hair-like structures that are covered with a sticky mucus, and trap dust and other inhaled particles. Co-ordinated wave-like beating of the cilia propels the mucus backwards towards the throat, where it is swallowed. Also seen are microvilli (green), which increase the cell's surface area. Magnification: x6000 when printed at 10 centimetres wide.