The |trachea|, or windpipe, is the upper section of the airway, separated from the |pharynx| by the |larynx|. It is composed of ribbed ~cartilage~ which extends about four inches down to the bronchii of the |lungs|. Resting flatly against the |esophagus|, the |trachea| can extend slightly during swallowing, breathing, or bending the neck. It is lined with a ~mucous~ layer and |cilia| which help to filter out dust. The constant action of these |cilia| carry ~mucous~ and debris upward into the |pharynx|, whereupon it is swallowed. When the upper |trachea| or |pharynx| become blocked so as to cut off the airway, as from swelling of the tissues, a small incision is made in the throat and into the |trachea|, in an operation called a tracheotomy, which allows ~air~ to pass into the windpipe.
