The Bronchial Tree

At the carina, located at the upper boundary of the fifth thoracic vertebra, the trachea splits into the right and left primary bronchi, each leading to its respective lung. The right primary bronchus is shorter, wider, and more vertical than the left one.

Similar to the trachea, both primary bronchi are composed of incomplete cartilage rings and ciliated pseudostratified columnar epithelium lining.

Upon entering the lungs, each primary bronchus branches into smaller lobar or secondary bronchi, with one bronchus serving each lobe in both lungs.

These lobar bronchi branch into smaller segmental bronchi, serving specific bronchopulmonary segments within the lobes.

The segmentation continues, forming bronchioles that branch into terminal bronchioles, marking the end of the conducting zone of the bronchial tree.

The bronchioles contain club cells or clara cells, a type of nonciliated columnar cells, which defend against inhaled toxins, may produce surfactant, and function as stem cells.

Additionally, branches of the bronchial tree have ciliated columnar and cuboidal epithelium, mucous-producing goblet cells, and a higher proportion of smooth muscles.