tracheas

The trachea, or windpipe, is a flexible airway that conducts air from the larynx to the bronchi. In humans and many mammals it measures about 10 to 12 centimeters in length and roughly 2 centimeters in diameter, though size varies with age and body size.

The walls of the trachea consist of C-shaped hyaline cartilage rings that keep the airway open. The open posterior portions are bridged by smooth muscle and connective tissue. The inner lining is pseudostratified ciliated columnar epithelium with goblet cells, resting on a thick elastic submucosa containing seromucous glands. The trachea is enveloped by an adventitia that blends with surrounding connective tissues.

Functionally, the trachea serves as a conducting passage for air and as part of the airway defense system. The mucociliary escalator traps inhaled particles in mucus and moves them toward the pharynx for expulsion, while the epithelium helps humidify and warm incoming air.

Branching and landmarks: The trachea extends from the larynx to the carina, where it bifurcates into the right and left main bronchi. The carina is a sensitive area that can trigger coughing when irritated. The bifurcation typically occurs around the level of the sternal angle, near the T4–T5 vertebral level in adults.

Development and variation: The trachea develops from the foregut during embryogenesis, with cartilage formation and mucosal lining maturing to form the adult airway. Across species, cartilage structure and gland distribution can vary. Clinically important issues include tracheal collapse, stenosis, trauma, infections, tumors, and foreign-body obstruction, as well as complications from intubation or bronchoscopic procedures. Imaging and endoscopy are common tools for evaluation.