Caption

Trachea lining. Black and white transmission electron micrograph (TEM) of a longitudinal section through the lining of the trachea (windpipe), which links the larynx (voicebox) to the lungs. The pseudo-stratified columnar epithelial lining consists of cells that have hair-like cilia (long) on their surface and mucus-secreting glands (not shown). Mucus secreted by the glands traps debris, such as dust particles or bacteria, in the inhaled air, while the beating of the cilia moves the mucus and particles upwards out of the respiratory tract, helping to keep the lungs and airways clear and prevent infection. Magnification: x2500 when printed 10 centimetres wide.