The main bronchi is the collective term given to the left and right main bronchi which are formed by the bifurcation of the trachea at the carina, supplying air to the right and left lungs respectively 1.
The main bronchi form part of the lower respiratory tract and are conducting airways, i.e. they purely help the air pass to and from the lungs. No gaseous exchange occurs in the main bronchi.
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 bronchopulmonary segment.
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Arterial supply
The main bronchi are supplied by the bronchial arteries.
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right main bronchus is supplied by one single right bronchial artery.
It arises from one of the following origins:proximal part of one of the upper posterior intercostal arteries (commonly right third posterior intercostal artery)
a common trunk with the left superior bronchial artery
the descending aorta
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left main bronchus is supplied by two arteries
superior and inferior left bronchial arteries directly arising from the descending aorta
Venous drainage
The main bronchi drain into the bronchial veins 2.
right main bronchus drains into the right bronchial vein which drains into azygos vein
left main bronchus drains into the left bronchial vein which drains into accessory hemiazygos vein
Radiographic features
Plain radiograph
Bronchus intermedius can be seen between the interlobar artery and right cardiac shadow. The left lower lobe bronchus is not usually seen because it lies behind the cardiac shadow. The pulmonary arteries are of the same diameter as the accompanying bronchi 1.
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