Left main bronchus
Bronchus principalis sinister
Also known as: left primary bronchus
The longer (≈5 cm), narrower and more horizontal main bronchus, passing beneath the aortic arch to the left lung.
Overview
The left main bronchus runs inferolaterally at ≈45° to the vertical, passing below the arch of the aorta and in front of the oesophagus and descending aorta to reach the left hilum, where it divides into the superior and inferior lobe bronchi. The left pulmonary artery arches over it (it has no eparterial bronchus), so on the left the artery is the most superior structure at the hilum.
Its length means that the left upper lobe bronchus arises well away from the carina, which is why left-sided double-lumen tubes are preferred for one-lung ventilation.
- Location
From the carina to the left hilum (≈T6), beneath the aortic arch.
Anatomy
- Relations
Superiorly: arch of the aorta and left pulmonary artery; posteriorly: oesophagus, descending aorta, thoracic duct; anteroinferiorly: left atrium; the left recurrent laryngeal nerve hooks under the aorta just above it.
Function
- Conducts air to the left lung (≈45% of total ventilation).
Clinical significance
Compression
Can be compressed by an aortic arch aneurysm (with a tracheal tug) or elevated by an enlarged left atrium (mitral stenosis), widening the carinal angle.
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.