Figure 1.

Tissue structure of the respiratory system. A variety of lung epithelial cells exist along the proximal‐distal axis. In proximal regions, there are five major cell populations, including basal cells (yellow triangle), Goblet cells (purple), ciliated cells (green), club cells (orange), and neuroendocrine cells (blue). The cellular composition varies along the proximal‐distal axis. Basal cells reside in only cartilaginous airways in mice, while they also reside in smaller airways, such as bronchioles, in humans. In alveolar regions, there are two types of epithelial cells: flattened alveolar type I cells (pale blue) and cuboidal alveolar type II cells (yellow)