Bronchi

A bronchus (plural: bronchi) is a major airway passage in the respiratory system that conducts air from the trachea into the lungs. The trachea bifurcates at the carina into the right and left main (primary) bronchi, each entering its respective lung at the hilum and branching into the Intrapulmonary bronchi with a dedicated hierarchy:.

• Lobar (secondary) bronchi three on the right (upper, middle, lower lobes) and two on the left (upper and lower lobes)

• Segmental (tertiary) bronchi supply individual bronchopulmonary segments (10 on the right, 8-10 on the left)

• Further subdivisions continue into smaller bronchi and eventually bronchioles (airways <1 mm in diameter lacking cartilage)

Histologicaly, bronchi are characterized by walls containing C-shaped or irregular cartilage plates, smooth muscle, submucosal glands, and a pseudostratified ciliated columnar epithelium (respiratory epithelium). As the airways branch and narrow, cartilage diminishes and smooth muscle becomes proportionally more prominent, until cartilage is absent in the bronchioles.