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Left Main Bronchus
Respiratory System

Left Main Bronchus

Bronchus principalis sinister

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Structure

The left main bronchus is formed at the bifurcation of the trachea into right and left main bronchi around the level of the sternal angle. It passes inferolaterally to reach the hilum of the left lung at the level of the sixth thoracic vertebra. Here, it divides into two lobar (or secondary) bronchi, the superior and inferior lobar bronchi.

The left main bronchus is narrower and twice as long as the right main bronchus. Additionally, it travels more horizontally than the right main bronchus; thus, inhaled objects are more likely to become lodged in the right main bronchus.

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Key Features/Anatomical Relations

As the left main bronchus courses from its origin at the distal end of the trachea to the hilum of the left lung, it passes under the aortic arch. Additionally, the left main bronchus passes anterior to the descending thoracic aorta and thoracic duct and is accompanied by the pulmonary artery and veins.

The left main bronchus forms part of the root of the lung. As it enters the hilum of the left lung, it lies inferior to the left pulmonary artery, posterior to the left superior pulmonary vein, and superior to the left inferior pulmonary vein.

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Main Bronchus

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The right main bronchus separates into superior, middle, and inferior lobar bronchi, each corresponding to the lobes of the right lung.

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