A bronchus (plural bronchi) is a tube in the respiratory tract that conducts air into the lungs.
The trachea (windpipe) divides into two main bronchi, the left and the right. The bronchi divide several more generations until they become bronchioles. There is a bronchus going to each segment of each lobe of the lung. Bronchi are generally greater than one millimetre in diameter.
There is still cartilage present in the bronchi, present as irregular rings in the larger bronchi, and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.