Mucous in the airway. Scanning electron micrograph (SEM) of mucous (blue) in the trachea. The trachea links the larynx to the lungs. The lining consists of mucus-secreting goblet cells and epithelial cells that are covered in hair-like cilia. Mucus 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. This helps to keep the lungs and airways clear and prevent infection. Magnification: x1500 when printed at 10cm bacteria