Trachea

Structure

The trachea is a tube-like structure that begins at the distal portion of the larynx, at the level of the sixth cervical vertebra. It extends inferiorly, passing from the neck, through the superior thoracic aperture and into the mediastinum.

The trachea bifurcates into the right and left main bronchi, most commonly at the sixth thoracic vertebra in 46% of individuals. However, this varies substantially from the lower end of the fourth to seventh thoracic vertebrae, and is higher in females (Standring, 2016).

In the adult, the trachea is typically 2 cm in diameter in males and 1.5 cm in females (Standring, 2016). It consists of 16–20 C-shaped rings of hyaline cartilage that occupy an anterolateral position in the tracheal wall. They are responsible for keeping the trachea patent for respiration to occur. Fibroelastic tissue, known as the tracheal annular ligaments, is interspersed between the cartilaginous rings. Posteriorly, the tracheal wall is flat and contains fibromuscular tissue, including the involuntary trachealis muscle (smooth muscle). The tracheal lumen is lined by a mucosa composed of pseudostratified ciliated columnar epithelium with goblet cells. The mucosa is thrown into folds along the posterior wall where hyaline cartilage is absent.

Anatomical Relations

The esophagus sits posterior to the trachea in the neck and superior mediastinum and separates it from the vertebral column. The flat, muscular posterior wall of the trachea accommodates the esophagus during swallowing to allow a food bolus to pass to the stomach.

The isthmus of the thyroid gland sits anterior to the trachea in the neck and is covered by the superficial and deep cervical fascia. In the thorax, the manubrium of the sternum, the origins of sternothyroid and sternohyoid muscles, thymus, and inferior thyroid veins also sit anterior to the trachea.

The lobes of the thyroid gland, the common carotid artery, and recurrent laryngeal nerves are all lateral relations of the trachea in the neck. The right lung, right vagus nerve, right brachiocephalic vein, superior vena cava, and azygos vein are right lateral relations of the trachea in the superior mediastinum. The aortic arch, left common carotid artery, left subclavian artery, and left recurrent laryngeal nerve are all located to the left of the trachea in the superior mediastinum.

Function

The trachea is integral to the respiratory system. It connects the larynx to the bronchial tree and allows air to flow between.

Arterial Supply

The trachea receives a blood supply from the inferior thyroid (in the neck) and bronchial (in the superior mediastinum) arteries.

Venous Drainage

The inferior thyroid venous plexus receives drainage from the trachea.

Innervation

The trachea receives autonomic innervation from the anterior and posterior pulmonary plexuses. The nerves of the pulmonary plexuses originate from the thoracic branches of the upper sympathetic trunk (sympathetic contribution) and the vagus nerve (parasympathetic contribution). For both sympathetic and parasympathetic fibers, axons may travel directly to the pulmonary plexus, or may travel through the cardiac plexus first. The autonomic innervation of the trachea controls airway function, such as tone of smooth muscle, mucus secretion, and vascular permeability and blood flow.

Lymphatic Drainage

The lymphatic drainage of the trachea is received by the paratracheal lymph nodes. The efferent vessels of the paratracheal lymph nodes unite with the parasternal and anterior mediastinal lymph vessels to form right and left bronchomediastinal trunks, which drain into the right lymphatic duct or thoracic duct, respectively.

List of Clinical Correlates

- Tracheostomy

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41 edn.: Elsevier Limited.