Development and Anatomy
Bronchus-associated lymphoid tissue (BALT) (below)--There is controversy about whether BALT is a structure analogous to Peyer's patches in the gut . Nevertheless, lymphoid aggregates, sometimes with germinal centers, can be found adjacent to airways from the trachea to the bronchioles. These aggregates have been related to past infection and cigarette smoking [8,9]. Structurally, they vary slightly from Peyer's patches, and their precise significance is not known.
This photo shows a lymphoid aggregate associated with a bronchiole.
Membranous bronchioles (below), characterized by circumferential epithelium and lack of cartilage, have cuboid epithelium. Goblet cells and bronchial glands are absent. Clara cells, which secrete a watery substance, appear in bronchioles. Normally, the lumen is rounded, and the subepithelial connective tissue and muscle are scanty. Multiple alveolar walls attached to the bronchiole serve to keep it open during expiration.
The photo shows a membranous bronchiole with continuous epithelium, a thin muscular layer, a small amount of connective tissue, and multiple alveolar wall insertions.
Normal postmortem bronchogram, right lung
The lung is oriented with the posterior portion down. Note the smooth tapering bronchial walls. Also note that the superior segment of the lower lobe begins posteriorly, making is most susceptible to aspirated material when a person is supine.