The trachea is a short, flexible air tube, which extends from the larynx down to the middle of the thorax, where it divides into two main bronchi.

The main function of the trachea is to provide the passage of air to and from the lungs. Additionally, it moistens and warms up the passing air, as well as participates in the coughing reflex.

The diameter of the trachea is about 0.6 - 1 inches (1.5 - 2.5 cm), and it is about 4 - 5 inches (10 - 13 cm) long in most people. Its size differs in men and women, as the trachea in males is typically wider and longer.

The trachea is composed of fifteen to twenty C-shaped cartilage rings, where the posterior part of each ring is made of muscle fibers and connective tissue. The muscle fibers throughout the trachea form the trachealis muscle.

The tracheal cartilages form the anterolateral wall of the trachea, while the trachealis muscle forms the posterior wall. The trachealis muscle allows the trachea to change its diameter mainly during swallowing when the food bolus (chewed food that is mixed with saliva) passes through the esophagus, which is located posterior to the trachea.

The trachea begins below the cricoid cartilage of the larynx, which is connected to the first tracheal cartilage by a fibrous structure called the cricotracheal ligament. Each two adjacent tracheal cartilages are joined by circular bands of fibrous connective tissue known as the annular ligaments.

The trachea is divided into two parts:

Cervical part - extends below the larynx as its continuation, starting from the lower border of the cricoid cartilage at the level of the sixth (in females) or seventh (in males) cervical vertebra (C6 - C7).
Thoracic part - begins at the level of the jugular notch as the trachea enters the rib cage through the superior thoracic aperture. Further, it passes behind the sternum and ends at the cartilaginous ridge called carina.

The carina of the trachea serves as a distributor of inhaled airflow between both main bronchi. It projects at the level of the fifth thoracic vertebra (T5), in the middle of the thorax. At this point, the trachea bifurcates dividing into the right and left main bronchi.

Neurovascular supply

The trachea receives arterial blood supply mainly from the tracheal branches of the inferior thyroid artery and ascending branches of the bronchial arteries.

Venous drainage is provided by veins that flow into the inferior thyroid venous plexus and further into the brachiocephalic veins.

The trachea is innervated by the vagus nerve (CN X) and the sympathetic trunk.

Parasympathetic and sensory innervation comes from the recurrent laryngeal nerves and other branches of the vagus nerve.
Sympathetic innervation originates from the sympathetic trunks and is provided by nerve fibers of the anterior and posterior pulmonary plexuses.

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Trachea