bronhi

Bronchi are the large air passages of the lower respiratory tract that conduct air from the trachea into the lungs. The plural term bronchi is commonly used in English; in some linguistic traditions, bronhi may be encountered as an alternative form. They form part of the bronchial tree, which distributes air to the lung lobes and lobular segments.

Anatomically, the trachea divides at the carina into two primary (main) bronchi, left and right. Each enters its respective lung and gives rise to lobar (secondary) bronchi for the lung lobes (three on the right, two on the left). These branch into segmental (tertiary) bronchi and progressively smaller bronchi, ultimately leading to the bronchioles. The walls of larger bronchi contain cartilage to keep the airways open, while smaller bronchi rely more on smooth muscle and structural support as cartilage diminishes.

Histologically, the bronchial mucosa is lined by pseudostratified ciliated columnar epithelium with goblet cells, which produce mucus. This epithelium is part of the mucociliary escalator that traps particles and moves mucus toward the pharynx. The submucosa contains mucous glands, and the amount of cartilage decreases with smaller bronchi, yielding to greater smooth muscle content that mediates airway caliber.

Functionally, bronchi conduct, warm, and humidify inspired air, while contributing to respiratory defense through mucus production and ciliary clearance. Autonomic nerves and local mediators regulate bronchial smooth muscle tone, influencing airway resistance during breathing.

Clinical relevance includes bronchitis (acute or chronic), asthma with reversible bronchial constriction, and other conditions such as bronchiectasis or obstruction. Diagnostic tools include bronchoscopy, imaging, and pulmonary function testing to assess bronchial structure and function. Bronchi receive blood supply from bronchial arteries and participate in the overall respiratory physiology alongside the alveolar regions.