The left bronchus is smaller in size but longer than the right bronchus, being nearly 5 cm. long.
The left bronchus enters the root of the left lung which is opposite to the sixth thoracic vertebra.
It then passes beneath the aortic arch, crosses in front of the esophagus, the thoracic duct, and the descending aorta, and has the left pulmonary artery lying at first above, and then in front of it.
The left bronchus has no eparterial branch, and therefore it has been supposed by some that there is no upper lobe to the left lung, but that the so-called upper lobe corresponds to the middle lobe of the right lung.
Both the left and right bronchus are shuttles that are extensions of the windpipe that send air to and from the lungs.
Oxygen goes through the left and right Bronchus and then carbon dioxide are left through them as well.