The<unk> rtes, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16cm. It commences at the larynx(at the level vertebral level of C6 in humans) and bifurcates into the primary (main) bronchi (at the vertebral level of T4/T5 in humans) in mammals, and from the pharynx to the syrinx in birds, allowing the passage of air to the lungs. It is lined with pseudostratified ciliated columnar epithelium cells with mucosae goblet cells which produce mucus. This lines the cells of the<unk>  to trap inhaled foreign particles which the cilia then waft upwards towards their larynx and then the pharynx where it can then be swallowed into the stomach.
In humans there are about 15 – 20 incomplete C-shaped cartilaginous rings which reinforces the anterior and lateral sides of the<unk>  to protect and maintain the airway open. There is a piece of smooth muscle connecting the ends off the incomplete cartilaginous rings called the<unk> lis muscle. This contracts reducing the size of the lumen of the<unk>  to increase the air flow rate during coughing. The esophagus lies posteriorly to the<unk> . The cartilaginous rings are incomplete because this allows the<unk>  to collapse slightly to allow food to pass down the esophagus. The epiglottis is the flap that closes the<unk>  during swallowing to prevent swallowed matter from entering the<unk> .
Vertebrate trachea
Upper respiratory tract
Pharynx
Muscles of larynx
Airway
Larynx
Nasopharynx
Throat