Bronchi are the main passageway 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. Primary bronchi are located in the upper portion of the lungs, with secondary bronchi near the center of the lungs. Tertiary bronchi are located near the bottom of these organs, just above the bronchioles. No gas exchanges occur in any of the bronchi. When the bronchi become swollen due to irritants or infection, bronchitis results and makes breathing more difficult. Bronchitis sufferers also tend to have much more mucus and phlegm than someone without inflamed bronchi.