Left main bronchus

Last revised by Patrick O'Shea on 3 Apr 2023

The trachea bifurcates into the right and left main bronchi at the level of the carina, supplying air to the right and left lungs respectively. Each main or primary bronchus enters the hilum of its lung and gives rise to secondary lobar bronchi, which further divide into tertiary segmental bronchi supplying the individual bronchopulmonary segments.

The left main bronchus is longer, runs more horizontally (40 degrees to the median plane) 3 and is about twice as long as the right main bronchus 1,2. It reaches the hilum of the left lung at the level of T6, lying inferior to the aortic arch and anterior to the esophagus and thoracic aorta.1,2 It is about 5 cm long and 1.2 cm in diameter.3

It gives rise to two lobar bronchi, the left upper and lower lobar bronchi 1.

At left pulmonary hilum:

The left main bronchus is supplied by two arteries, the superior and inferior left bronchial arteries arising directly from the descending aorta 2.

The left main bronchus drains into the left bronchial vein which drains into the accessory hemiazygos vein 5.

The left main bronchus is most often elliptic in shape on its cross section.4

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Cases and figures

  • Figure 1: left sided bronchi
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  • Figure 2: annotated CT
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  • Figure 3: lymphatics of the tracheobronchial tree (Gray's illustration)
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