How does the structure of the bronchial tree change as the bronchi become smaller?

The following structural changes occur as conducting tubes become smaller;

- support structures change. The trachea has more hyaline cartilage than the bronchioles

- epithelium type changes with bronchioles having ciliated columnar cells with the trachea having tall       columnar pseudostratified

- amount of smooth muscle increases as you go lower the respiratory tract

correct answer is a. and d.