Trachea lining. Coloured scanning electron micrograph (SEM) of a section through the lining of the trachea (wind pipe). The trachea links the larynx (voice box) to the lungs. Across upper frame are pseudostratified ciliated columnar epithelial cells (bright orange), which line the trachea. The hair-like cilia (yellow) on their surface beat to move mucous, and particles trapped in it, upwards out of the respiratory tract. This helps to keep the lungs and airways clear and prevent infection. At bottom is the basement membrane, a layer of connective tissue that supports the epithelial cells.