Comparison of species differences in proximal intrapulmonary airways
| Parameter | Human | Monkey | Mouse |
| Wall | |||
| Smooth muscle | Present | Present | Present |
| Cartilage | Present | Present | Absent |
| Submucosal glands | Present | Present | Absent |
| Epithelium | |||
| Thickness μm | 40–50 | 27 | 8–16 |
| Cells per mm basement membrane | NA | 175 | 109 |
| Mucous goblet cells % | 10 | 15 | <1 |
| Serous cells % | 3 | 5 | <1 |
| Clara cells % | 61 | ||
| Ciliated cells % | 37 | 47 | 36 |
| Basal cells % | 32 | 32 | <1 |
| Other % | 18 | 2 | 2 |