Bronchus histology

Almost the entire respiratory tree, from the nose to the bronchi, is lined on the inside with a tissue that has a difficult name: pseudostratified ciliated columnar epithelium. It is worth taking apart. Columnar, because its cells are tall. Ciliated, because they have moving hairs called cilia. And pseudostratified, which means falsely layered: it is really a single layer of cells resting on the basement membrane, but because their nuclei do not sit at the same height, under the microscope they look like several layers.

Among those cells are some shaped like cups, the goblet cells, which release mucus. That mucus is the first line of defense against the pathogens that come in with the air: particles get stuck in it, and then the cilia push them up and out, like an escalator that never stops going up. And along the widest stretch of that path, the trachea and the bronchi also have rings of hyaline cartilage that support those large passages.