FIG 1.

General epithelial populations in mammalian lungs. Pseudostratified epithelium is observed in the trachea of both human and mice. Basal cells are situated on basal membrane and serve as stem cells. Basal cells are restricted to the tracheal region in mice but distributed from proximal to distal axis in human lungs. Club cells and ciliated cells represent two of the most predominant cell types in conducting airways. Bronchioalveolar stem cells (BASCs) are found in distal conducting airways of mice but not human. Alveolar epithelia in human is similar to that in mice, including AT1 and AT2 cells. Markers and functions of each epithelial cell type are also indicated.