[trey-kee-uh or, especially Brit., truh-kee-uh]
trachea or windpipe, principal tube that carries air to and from the lungs. It is about 41/2 in. (11.4 cm) long and about 3/4 in. (1.9 cm) in diameter in the adult. It extends from the larynx to the bronchial tubes and is situated in front of the esophagus (see respiration). The trachea consists of a supporting layer of connective and muscular tissue in which are embedded from 16 to 20 U-shaped rings of hard cartilage that encircle the front of the tube. Tiny hairs, or cilia, in the mucous membrane lining keep dust and other foreign particles from entering the lungs. The foreign material becomes trapped in the mucus and is swept by the beating cilia to the nose or mouth, where it is discharged from the body. The air tubes of insects and other arthropods are also called trachea.
or windpipe

Tube in the throat and upper thoracic cavity through which air passes in respiration. It begins at the larynx and splits just above heart level into the two main bronchi, which enter the lungs. In adults it is about 6 in. (15 cm) long and 1 in. (2.5 cm) in diameter. Its structure—a membrane strengthened by 16–20 cartilage rings open in the back, with their free ends connected by muscle bands—allows the trachea to stretch and contract in breathing. An inner mucous membrane has cilia (see cilium) that project inward to trap particles. Muscle fibres over and alongside the trachea contract in response to cold air or irritants in inhaled air; in coughing, the airway narrows to about one-sixth of its normal size to increase the speed and force of exhalation and to dislodge foreign bodies. Such diseases as diphtheria, syphilis, tuberculosis, and typhoid often involve the trachea.

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Trachea is a common term for an airway through which respiratory air passes in organisms.

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