Trachea

Trachea

Also known as: windpipe

A flexible 10–12 cm tube held open by 16–20 C-shaped hyaline cartilage rings, running from the cricoid cartilage (C6) to its bifurcation at the carina (T4/T5).

Show on body map Respiratory Tract

Overview

Length≈10–12 cm

Internal diameter≈1.5–2.5 cm

Cartilage rings16–20

ExtentC6 → T4/T5 (sternal angle)

The trachea begins at the lower border of the cricoid cartilage and descends in the midline, slightly to the right, through the neck and superior mediastinum to divide into the right and left main bronchi at the level of the sternal angle. It is ≈2 cm wide in adults (smaller in women) and very mobile: it lengthens and descends during inspiration and rises with the larynx in swallowing.

Its C-shaped hyaline cartilage rings prevent collapse during the pressure swings of breathing and coughing. They are open posteriorly, where the gap is bridged by a fibroelastic membrane and the smooth-muscle trachealis, which lies against the oesophagus — allowing the oesophagus to bulge forward as a bolus passes, and narrowing the lumen during coughing to increase air velocity.

Location: Anterior neck and superior mediastinum, from C6 to T4/T5; anterior to the oesophagus.

Parts & subdivisions

Cervical part
From C6 to the jugular notch (≈T2); covered by the thyroid isthmus at rings 2–4, pretracheal fascia, strap muscles and the jugular venous arch.
Thoracic part
In the superior mediastinum, from the jugular notch to the carina at T4/T5.
Tracheal cartilages
16–20 C-shaped hyaline rings; the first is broader and the last forms the carina.
Trachealis and membranous wall
Smooth muscle and fibroelastic tissue closing the posterior gap of each ring.
Carina
Keel-shaped ridge at the bifurcation.

Anatomy

Innervation: Vagus (recurrent laryngeal and direct branches): parasympathetic secretomotor and bronchoconstrictor fibres to glands and trachealis, plus sensory fibres (cough). Sympathetic fibres from the cervical and upper thoracic sympathetic trunk.
Arterial supply: Cervical part: tracheal branches of the inferior thyroid arteries. Thoracic part: bronchial arteries (with contributions from the internal thoracic arteries).
Venous drainage: Inferior thyroid veins → brachiocephalic veins; bronchial veins.
Lymphatic drainage: Pretracheal and paratracheal lymph nodes → deep cervical nodes; tracheobronchial nodes in the thorax.
Relations: Neck: anteriorly thyroid isthmus, inferior thyroid veins, strap muscles; laterally thyroid lobes and common carotid arteries; posteriorly oesophagus with the recurrent laryngeal nerves in the tracheo-oesophageal grooves. Superior mediastinum: anteriorly manubrium, thymic remnants, left brachiocephalic vein, brachiocephalic trunk and left common carotid artery; on the right the right vagus, azygos arch, SVC and right pleura; on the left the arch of the aorta, left common carotid and subclavian arteries and the left recurrent laryngeal nerve.
Histology: Four layers: mucosa (respiratory epithelium — ciliated, goblet, basal, brush and neuroendocrine cells — on a thick basement membrane, with an elastic lamina propria); submucosa with seromucous glands; hyaline cartilage rings with perichondrium; adventitia.
Development: From the laryngotracheal tube (endoderm) separated from the oesophagus by the tracheo-oesophageal septum in weeks 4–5; cartilage and muscle from splanchnic mesoderm.

Function

Conducts air between the larynx and the main bronchi.
Traps and clears inhaled particles by mucociliary transport towards the larynx.
Warms and humidifies air; triggers the cough reflex.

Clinical significance

Tracheal deviation

The trachea is normally central in the jugular notch. It is pushed away by tension pneumothorax, large effusion or a mass, and pulled towards collapse (lobar or total), pneumonectomy or upper-lobe fibrosis.

Tracheostomy

An opening into the trachea, usually through rings 2–4 (dividing or retracting the thyroid isthmus), used for prolonged ventilation or upper-airway obstruction. Hazards include the inferior thyroid veins, thyroidea ima artery and, in children, the brachiocephalic vessels; late tracheal stenosis can follow.

Tracheo-oesophageal fistula

Developmental failure of the tracheo-oesophageal septum (see system development): coughing and cyanosis with feeds, recurrent aspiration pneumonia.

Test yourself

After a stab wound, a patient is hypotensive with distended neck veins, absent breath sounds on the right and a trachea deviated to the left. What is the immediate management?

Needle decompression of the right hemithorax
Chest radiograph to confirm
Pericardiocentesis
Intubation and positive-pressure ventilation

Answer: Needle decompression of the right hemithorax

This is a tension pneumothorax — a clinical diagnosis. Air trapped in the right pleural space shifts the mediastinum to the left and obstructs venous return. Immediate needle decompression (then a chest drain) is life-saving; waiting for imaging or starting positive-pressure ventilation first can be fatal.

The tracheal bifurcation (carina) lies at approximately which level?

C6 vertebra
Jugular notch
T4–T5 intervertebral disc (sternal angle)
T8 vertebra

Answer: T4–T5 intervertebral disc (sternal angle)

The trachea begins at the lower border of the cricoid cartilage (C6) and bifurcates at the plane of the sternal angle (T4/T5) — slightly lower (down to T6) in the living upright subject during inspiration.