What is the anatomy of the trachea?

Tracheal Anatomy

Basic Structure and Dimensions

The trachea is a 12 cm fibrocartilaginous tube extending from the lower border of the cricoid cartilage to the carina, where it bifurcates into the mainstem bronchi, with a cross-sectional area of approximately 2.5 cm² in adults. 1, 2

• The trachea is formed by 16-20 U-shaped cartilaginous rings anteriorly and laterally, with the posterior wall closed by the trachealis muscle (a smooth muscle membrane). 3, 4
• It represents generation 0 in the airway hierarchy, serving as the entrance point to the sequential dichotomous branching system that ultimately connects to approximately 100 m² of alveolar gas exchange surface. 2
• The trachea is generally a midline structure, though it is displaced slightly to the right by the aortic arch. 5

Anatomical Relationships

The trachea occupies a critical position in the neck and superior mediastinum, with important relationships to surrounding vascular and visceral structures.

• The trachea extends from the level of the C6 vertebra (cricoid cartilage) to approximately the T4-T5 vertebral level (carina). 4
• Posteriorly, the trachea is intimately related to the esophagus, creating the tracheoesophageal stripe visible on imaging. 5
• The right and left paratracheal stripes represent important radiographic landmarks formed by the interface between the trachea and adjacent mediastinal structures. 5
• The trachea can be displaced, bowed, or indented by mediastinal masses (particularly thyroid masses), vascular anomalies (such as right-sided aortic arch), or enlarged lymph nodes. 5

Histological Structure and Function

The tracheal wall consists of multiple functional layers designed to facilitate air flow, mucociliary clearance, and humidification.

• The mucosa contains pseudostratified ciliated columnar epithelium with goblet cells and recently described cholinergic chemosensory cells. 1, 4
• Submucosal tracheal glands produce mucus that, combined with ciliary action, creates the mucociliary escalator for airway clearance and pulmonary defense. 1, 4
• The cartilaginous framework maintains airway patency during respiration while allowing flexibility during swallowing and neck movement. 4
• Different types of stem cells reside in the mucosal epithelium and glandular ducts throughout adult life. 1

Functional Significance

The trachea serves four primary functions: conduit for air flow, apparatus for phonation, mucociliary clearance system, and humidification/warming of inspired air. 1, 4

• As a conducting airway, the trachea has a multilayered wall with mucous membrane, smooth muscle, and cartilage, distinguishing it from more distal acinar airways. 2
• The trachea provides excellent intrinsic contrast on imaging due to the air-tissue interface, making it one of the most easily visualized intrathoracic structures. 5
• Tracheostomy tubes placed through the anterior tracheal wall reduce resistive and elastic work of breathing compared to translaryngeal endotracheal tubes by lessening inspiratory and expiratory airways resistance. 6

Clinical Considerations

In pediatric patients, the trachea is small, pliable, and difficult to palpate, with the pleura extending into the neck, creating unique technical challenges for tracheostomy procedures.

• The small tracheal diameter in children necessitates vertical tracheotomy rather than cartilage window techniques to avoid creating stenotic segments. 2
• The trachea's position as generation 0 means that any obstruction at this level has immediate and severe consequences for ventilation, as there are no alternative pathways for air flow. 2
• For speech production in tracheostomy patients, the tracheal cannula must not exceed two-thirds the lumen of the anatomical trachea to allow adequate air leak around the tube for phonation. 2