Bronchi and Bronchial Tree

The bronchi are the large airways that branch off the bottom of the trachea and carry air into the lungs. Together with their progressively smaller branches, they form the bronchial (or tracheobronchial) tree, an upside-down, tree-like network of tubes that distributes air throughout each lung.

Gross Structure and Location

At the carina, the trachea splits into the right and left main (primary) bronchi, one entering each lung at the hilum. The right main bronchus is wider, shorter, and more vertical than the left, which is why inhaled objects more often lodge on the right side. Inside the lungs, each main bronchus divides into lobar (secondary) bronchi, one for each lobe: three on the right and two on the left. These divide further into segmental (tertiary) bronchi that supply the bronchopulmonary segments, then into smaller bronchioles. Larger bronchi contain cartilage plates and smooth muscle in their walls; as the airways narrow into bronchioles, cartilage disappears and smooth muscle becomes more prominent.

Key Functions

The bronchial tree's main role is to conduct air deep into the lungs and distribute it evenly to the alveoli, where gas exchange occurs. The smooth muscle in the bronchial and bronchiolar walls can contract or relax to adjust airway diameter and regulate airflow. Like the trachea, the bronchi are lined with ciliated, mucus-producing cells that trap particles and sweep them upward as part of the mucociliary clearance system that protects the lungs.

Clinical Relevance

The bronchi are central to several common diseases. In asthma, the bronchial smooth muscle tightens and the lining swells, narrowing the airways and causing wheezing and shortness of breath. Bronchitis is inflammation of the bronchial lining, often from infection or smoking. In chronic obstructive pulmonary disease (COPD), chronic inflammation damages the airways. Bronchiectasis is permanent widening and scarring of the bronchi. Because the airways are accessible, doctors use bronchoscopy, passing a thin camera through the airways, to inspect the bronchi, take biopsies, and remove blockages.

This page is educational and not a substitute for professional medical advice.