In which parts of the airway does cartilage disappear?

• A. In the trachea only
• B. Throughout the entire respiratory tract
• C. Beyond the bronchi, in the bronchioles (progressively to terminal bronchioles)
• D. Only in the alveoli

Answer: (C)

Cartilage provides rigid support for keeping the airways open in the early conducting passages. In the trachea and the larger bronchi you see cartilage—tracheal rings and bronchial plates help hold those tubes open. As you move toward smaller airways, that cartilage disappears; beyond the bronchi, in the bronchioles, there is no cartilage at all, and this absence continues through the terminal bronchioles. This loss of cartilage is what allows the bronchioles to be regulated by smooth muscle to adjust airflow. The alveoli are not supported by cartilage, since they are delicate sacs for gas exchange rather than conduits for airflow.