The airway is split into left and right branches known as the primary bronchi at the lower end of the trachea. Before branching off into smaller secondary bronchi, the left and right bronchi lead into each lung. The secondary bronchi carry air into the lobes of the lungs, with two being in the left lung, and three in the right lung (making it the larger lung). Then, in turn, the secondary bronchi split into many smaller tertiary bronchi within each lobe, which also split into several smaller bronchioles that are spread throughout the lungs. This pattern continues until each bronchiole is split into “terminal bronchioles” that are extremely small- approximately one millimeter or less in diameter. Finally, the millions of tiny terminal bronchioles
