A bronchus (plural bronchi, adjective bronchial) is a caliber of airways in the respiratory tract that conducts air into the lungs. No gas exchange takes place in this part of the lungs.

Anatomy

The trachea (windpipe) divides into two main bronchi, the left and the right. These subdivide in two (left lung) or three (right lung) bronchi that each serve one lobe. 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 not as regular as in the trachea), and as small plates and islands in the smaller bronchi. Smooth muscle is present continuously around the bronchi.

Role in disease

Bronchitis is viral or bacterial infection of the bronchi. Asthma is hyperreactivity of the bronchi with an inflammatory component, often in response to allergens. Chronic bronchitis (COPD) is smoking- or coal dust-induced chronic inflammation of the bronchi that leads to obstruction of the airways.