Comparison of species differences in cells of the trachea
| Parameter | Human | Monkey | Mouse |
| Wall | |||
| Smooth muscle | Present | Present | Present |
| Cartilage | Present | Present | Present |
| Submucosal glands | Present | Present | Present (proximal 1/3) |
| Epithelium | |||
| Thickness μm | 50–100 | 20–30 | 11–14 |
| Cells per mm basement membrane | 303±20 | 181±51 | 215 |
| Mucous goblet cells % | 9 | 17 | <1 |
| Serous cells % | <1 | <1 | |
| Clara cells % | <1 | 49 | |
| Ciliated cells % | 49 | 33 | 39 |
| Basal cells % | 33 | 42 | 10 |
| Other cells % | 8 | 1 |