The windpipe; the connection from the pharynx to the lungs. The trachea is protected by rigid C-shaped rings of cartilage in the front and sides, keeping the passage open during inhalation. These rings are softer in younger children.

A sick patient; the medical state when a patient is at risk for death in the near future.

A blood vessel that carries blood back to the heart. Veins carry de- oxygenated blood (except for the pulmonary veins

 A whistling sound made by narrowing of the small airways heard most commonly in patients with asthma and emphysema.