Bronches

Bronches, commonly referred to as the bronchi, are the main air passages of the lungs that branch from the trachea and distribute air to the lungs. They form the upper part of the bronchial tree and divide into progressively smaller passages as they extend into each lung.

Anatomy and structure: The two main bronchi are the right main bronchus and the left main bronchus. The right main bronchus supplies the right lung and typically divides into three lobar (secondary) bronchi, while the left main bronchus divides into two lobar bronchi to serve the left lung. Each lobar bronchus further subdivides into segmental (tertiary) bronchi that supply bronchopulmonary segments. The walls of larger bronchi contain cartilage to maintain openness; the mucosa is lined by pseudostratified ciliated columnar epithelium with goblet cells. Beneath the mucosa lies the submucosa with mucus-producing glands. As bronchi branch and become smaller, cartilage diminishes and smooth muscle becomes more prominent, allowing regulation of airway diameter.

Function: Bronchi conduct and condition inhaled air, warming and humidifying it and filtering particulates. The ciliated epithelium and mucus glands support mucociliary clearance, moving mucus and trapped debris toward the throat for expulsion or swallowing.

Clinical relevance: Conditions affecting the bronchi include acute and chronic bronchitis, asthma (bronchial hyperreactivity and constriction), bronchiectasis, and chronic obstructive pulmonary disease. Obstruction, infection, or excessive inflammation of the bronchial tree can impair ventilation and gas exchange. Treatments often target inflammation and bronchial tone using inhaled medications and supportive therapies.

Development: Bronchi originate from the foregut endoderm, with mesenchymal components forming supporting cartilage and smooth muscle during embryonic development.