The trachea is the organ of the respiratory system that connects the larynx with the initial portion of the bronchi, where it splits at the fifth thoracic vertebra, sharing in both the left and right bronchial trees. The bifurcation is called bronchial hull or tracheal spur. Moreover, the trachea allows the passage of air.

What is the trachea?

The trachea is located in front of oesophagus and shaped like a hollow cylinder with a length of approximately 12 cm. The trachea is constituted by a superposition of cartilage in the shape of a horseshoe placed horizontally and superimposed on each other. Between the cartilages there are interposed fibrous structures called ligaments or tracheal annular ligament. The rear part, formed by the openings of the cartilages, is closed by muscle tissue. The external composition involves tissue that is fibro cartilaginous, while internally the walls are covered with mucous.

At the base of the mucous membrane the network of tissue made up of elastic and collagen fibres aids in the contraction, expansion and stability of the tracheal walls. Moreover, there are a large number of blood and lymphatic vessels in this mucous layer. The blood vessels regulate heat exchange and cellular maintenance, while the lymphatic vessels are responsible for removing foreign particles that were collected by the surface of the tracheal wall.

The lateral aspects of the trachea receive blood supply through longitudinal vascular anastomoses of interconnected branches along the lateral surface area of the trachea. The anastomoses include the inferior thyroid artery, supreme intercostal artery, internal thoracic artery, brachiocephalic trunk, subclavian artery, and bronchial arteries located at the tracheal bifurcation. Moreover, the lateral and anterior tracheal walls receive blood supply through transverse segmental vessels found in the soft tissues between the cartilages. The transverse segmental vessels interconnect the longitudinal anastomoses across the midline of the trachea and supply the submucousal capillary network.

The innervation of the muscle fibres of the trachea is provided through the recurrent laryngeal nerve. Related to the recurrent laryngeal nerve are sympathetic nerve fibres derived primarily from the middle cervical ganglion.

There are several diseases that can affect the trachea: the most common are tracheitis, infections that can be acute or chronic, whose causes can be viral, bacterial, and allergic.

What function does the trachea serve?

The main functionality of the trachea is to allow the passage of air from the larynx to the bronchial tubes.

Moreover, the trachealis muscle located in the posterior wall aids the trachea to contract and reduce in diameter, which makes coughing more forceful and more effective. In the process of swallowing the oesophagus needs to expand, which is possible due to the incomplete cartilage rings of the trachea that allow it to narrow in order for the oesophagus to expand into the space of the trachea.

Finally, the loose attachment of the adventitia (the outermost layer of the wall of a blood vessel) allows the trachea to move within the neck and thorax, which may aid the lungs during contraction and expansion while breathing.