Final answer:
The trachea features C-shaped rings of cartilage that keep the airway open. From bronchi to bronchioles, cartilage decreases, the walls become thinner, and the airways become more numerous leading to the alveoli for gas exchange.
Step-by-step explanation:
A significant structural feature of the trachea that keeps the airways open is the stack of C-shaped rings of hyaline cartilage. These rings ensure that the trachea remains open for air to pass through to the lungs. As we move from the bronchi to the bronchioles, the structural changes include a reduction in cartilage support, and the walls of the tubes becoming thinner and more muscular. The airways decrease in size but increase in number, which aids in the distribution of air to the large surface area in the lungs necessary for gas exchange.
The bronchi branch into the right and left primary bronchi at the carina, lined by pseudostratified ciliated columnar epithelium and supported by rings of cartilage. As the bronchi continue to branch inside the lungs, they form the bronchial tree and eventually become bronchioles, which lack the cartilage that is characteristic of the larger bronchi. The bronchioles then lead to the alveoli, where gas exchange occurs.