A bronchus (plural bronchi, adjective bronchial) is one of two large tubes at the bottom of the trachea. The left bronchus leads to the left lung and the right bronchus leads to the right lung. Each bronchus—the name for just one bronchi—branches into smaller and smaller bronchial tubes. No gas exchange takes place in this part of the lungs. Bronchioles are the tiniest bronchial tubes. Each lung has about 30,000 bronchioles that are about the same thickness as a hair.
The trachea divides into two main bronchi, the left and the right. The right main bronchus is wider, shorter, and more vertical than the left main bronchus. The right main bronchus subdivides into three segmental bronchi while the left main bronchus divides into two.