Comparison of species differences in terminal bronchioles
| Parameter | Human | Monkey | Mouse |
| Wall | |||
| Cartilage | Absent (bifurcation) | Absent (bifurcation) | Absent |
| Smooth muscle | Present | Present | Present |
| Submucosal glands | Absent | Absent | Absent |
| Epithelium | |||
| Thickness | ? | ? | 7–8 |
| Cells per mm basement membrane | ? | ? | ? |
| Mucous goblet % | 0 | ||
| Serous cells % | 35 | ∼20 | 0 |
| Clara cells % | 60–80 | ||
| Ciliated cells % | 52 | ∼50 | 40–20 |
| Basal cells % | <1 | ∼10 | <1 |
| Other % | 13 | ∼ 5 | 0 |