The airway which measures about 1 inch in diameter is maintained by a series of C shaped rings made of cartilage. These rings are incomplete to allow the trachea to collapse during times when food is swallowed into the esophagus which leads to the stomach.

There is a epiglottis flap-like type structure atop the larynx known as the voice box that opens and closes depending on whether air is passing over it or whether food or liquid is being swallowed.

When a person coughs the trachealis muscle connects these incomplete C shaped rings allowing the trachea to contract and by doing so increases the airflow rate. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus.

The mucus lines the cells of the trachea to capture foreign particles (such as dust, mold, and pollen). The cilia which are hairlike protrusions extending from the trachea then waft upward toward the larynx and then the pharynx where it can be swallowed into the stomach or expelled by coughing. This mucus that is produced is called phlegm.

The length of the trachea can vary from 3.9 inches to 6.3 inches. The trachea starts at the lower part of the larynx level with the sixth cervical vertebra, and continues toward the primary bronchi where it bifurcates (to divide into two branches) at the vertebral level of the thoracic vertebra T5. It can vary in this position up to two vertebrae lower or higher depending on the breathing. The esophagus lies posterior to the trachea. The goblet cells which line the trachea have one sole purpose which is to secrete mucin which dissolves in water to become mucus. The epiglottis in humans is also a speech organ.