Main bronchus: anatomy, location and function

What it is

The left main (primary) bronchus, one of the two airways formed by the division of the trachea.

Location

It runs from the tracheal bifurcation (carina) at about T4–T5 downward and laterally to the hilum of the left lung, passing below the arch of the aorta and in front of the oesophagus and descending aorta.

Function

It conducts air from the trachea into the left lung and divides into the superior and inferior lobar bronchi.

Body system

Respiratory · paired (left and right)

FMA ID

FMA7396 (Foundational Model of Anatomy)

Key facts

• It is about 5 cm long, twice the length of the right main bronchus, and narrower.
• It leaves the trachea at a wider angle from the vertical (about 40 to 45 degrees) than the right (about 25 degrees), so it runs more horizontally; the heart and aortic arch push it sideways.
• The left pulmonary artery arches over it at the hilum.
• The left lung has 8–10 bronchopulmonary segments, depending on whether the apicoposterior and anteromedial basal segments are counted as one or two.

Clinical relevance

Inhaled foreign bodies lodge less often here than on the right, because the left bronchus is narrower and more oblique.

The nearest named structures in the 3D model, measured from the centre of each part:

• Main bronchus proper · respiratory
• Pulmonary artery · cardiovascular
• Accessory hemiazygos vein · cardiovascular
• Superior pulmonary vein · cardiovascular
• Esophagus · digestive
• Cavity of atrium · cardiovascular
• Great cardiac vein · cardiovascular
• Fourth rib · skeletal
• Posterior cusp of aortic valve · cardiovascular
• Inferior pulmonary vein · cardiovascular