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

A bronchus, also known as a main or primary bronchus, is a passage of airway in the respiratory tract that conducts air into the lungs. There is a right bronchus and a left bronchus and these bronchi branch into smaller secondary and tertiary bronchi which branch into smaller tubes, known as bronchioles.

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