Bronchial mucosal cells.

The eight epithelial cell types and their features are described--the basal, Kultschitzsky, intermediate, brush, ciliated, serous, Clara, and mucous cell. In the irritated airway the separate secretory cell types are able to change, through transitional cell types, from the Clara and the serous to the mucous cell. Each type of epithelial cell may be associated with intraepithelial nerves, including sensory and motor, some adrenergic, some cholinergic. The epithelial surface is covered with a periciliary fluid layer in which the cilia beat. Turnover time of the epithelial cell population is faster in the young animal than old, in male than female, and in extrapulmonary than intrapulmonary airways. The epithelium responds differently to the first single exposure to tobacco smoke--in extrapulmonary airways a 'discharge' effect causes a fall in the apparent number of secretory cells while in intrapulmonary airways secretory cell number increases. Further exposures increase the secretory cell number to its maximum more rapidly in extrapulmonary than intrapulmonary airways. Differences between the response of the secretory cell population to isoproterenol and salbutamol indicate differences in the beta-adrenergic receptors in different airway regions.