The trachea is the first part of the lower respiratory tract and forms part of the conducting part of the respiratory system. It extends from the inferior edge of the larynx until it bifurcates into the main bronchi at the carina. 

Development

The lower respiratory organs develop as an out-pocketing of the foregut endoderm. This protrusion is called the laryngotracheal bud and is present by the fifth week of development. The proximal part of the bud forms the tracheal lining.

 

Surface Anatomy

The trachea is a midline structure in the neck and is palpable in the jugular notch as it enters the superior mediastinum.

 

Macro-Anatomy (e.g. lobes, surfaces, impressions etc)

The trachea extends from the cricoid cartilage, at the level of C6 and terminates at the carina. The carina is the point at which the trachea bifurcates into the right and left main bronchi and is at the level of the sternal angle of Louis (T4/5).

 

It is 12cm long and is 1.6 – 2 cm in diameter. Due to its elasticity during inspiration, the trachea can extend to 15cm in length and in deep inspiration bifurcates at the level of T6.

 

It is composed of 12-20 C-shaped hyaline cartilage rings that maintain the trachea’s patency and is completed posteriorly by the trachealis muscle.

 

Anatomically, the trachea has 2 parts: the cervical trachea (from C6 to the sternal notch at T2/3) and the thoracic trachea lying in the superior mediastinum. This is important with regards to the relations of each as outlined below.

 

Cervical portion relations:

·       Anterior: thyroid isthmus, inferior thyroid veins, strap muscles and cervical fascia

·       Lateral: carotid sheaths, lobes of the thyroid gland

·       Posterior: oesophagus with the recurrent laryngeal nerves lying in the groove between trachea and oesophagus

 

Thoracic portion relations:

·       Anterior: cardiac plexus, aortic arch, left innominate vein, remains of thymus and sternum

·       To the left: recurrent laryngeal nerve, aortic arch, left common carotid and subclavian arteries, pleura

·       To the right: vagus nerve, azygos vein, pleura

·       Posteriorly: oesophagus

 

Micro-Anatomy (e.g. cell types, histology etc)

The trachea is lined by pseudostratified ciliated columner epithelium with mucus producing goblet cells. The mucus layer warms and humidifies the air, and traps inhaled particles which are then propelled to the pharynx by the cilia where they are swallowed.

 

Blood Supply

Blood supply to the trachea is from inferior thyroid, bronchial and internal thoracic arteries.

Venous drainage is via the inferior thyroid veins.

 

Nerve Supply (link to dermatome and referred pain as appropriate)

Sensation is from the vagus nerve (cranial nerve X)

 

Physiology (e.g. functions, relationships to other body systems)

 

The trachea’s primary function is to conduct air from the larynx to the bronchial tree. It is also involved in mucociliary clearance and humidification of the air as described above.

 

The vagus nerve forms the afferent branch of the cough reflex. Efferent fibres contract the trachealis muscle to reduce the diameter of the trachea and increase the flow through it, helping to clear mucus from the trachea when we cough. 

Development	Foregut endoderm
Blood vessels	Inferior thyroid, bronchial and internal thoracic arteries
Nerves	Inferior thyroid veins
Lymphatics	Vagus nerve (CN X)

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The trachea is the first part of the lower respiratory tract providing a route for the passage of air into the alveoli, connecting the pharynx to the main bronchi. Forming in the second month of development, knowledge of its development from the foregut endoderm enables the understanding of congenital malformations in the form of trachea-oesophageal fistulas.

Drake RL, Vogl W, Mitchell AWM. 2005. Gray’s Anatomy for students. Churchill Livingstone

 

Ellis H, Mahadevan V. 2010. Clinical Anatomy: Applied anatomy for students and junior doctors. Wiley-Blackwell

 

Marieb EN, Hoehn K. 2007. Human Anatomy and Physiology. Pearson Benjamin Cummings