Bronchi are the main passageway of air into the lungs.
When someone takes a breath through their nose or mouth, the air travels into the larynx. The next step is through the trachea, which carries the air to the left and right bronchus. The bronchi become smaller the closer they get to the lung tissue and are then considered bronchioles. These passageways then evolve into tiny air sacs called alveoli, which is the site of oxygen and carbon dioxide exchange in the respiratory system.