Morphologic features of airway surface epithelial cells and glands.

Both the epithelium and submucosal glands of the conducting airways of the lung are composed of a variety of recognizable cell types as determined by light and electron microscopy. The morphologic features that allow a classification of these cell types to be made are summarized herein as are the occurrence and species distribution of each cell type. Many, but not all, of the epithelial cell types are found in humans, but their occurrence, frequency, and species distribution vary. The total volume and airway distribution of submucosal glands are also species specific. Although the cell types of the gland have been well described in humans and the opossum, little is known of their morphologic aspects in other species. The suggested and possible functions for the cell types recognized are many and are tabulated for discussion. Extrapolation to humans from the results of animal studies requires caution and should be based on judicious choice of animal species with a full knowledge of comparative structure. The aim of this report is to highlight species differences in airway mucosal structure so that the choice of an appropriate animal model may be made more easily.