What is the key structural difference between bronchi and bronchioles?

• A. Bronchi have cartilage and submucosal glands; bronchioles lack cartilage and glands.
• B. Bronchioles have cartilage and glands; bronchi do not.
• C. Bronchioles have cartilage; bronchi do not.
• D. Bronchi are without glands.

Answer: (A)

Bronchi and bronchioles differ in how their walls are supported and how mucus is produced. Bronchi are larger airways that keep themselves open with cartilage in their walls and contain submucosal glands that secrete mucus. This combination helps prevent collapse and assists in filtering and humidifying air. Bronchioles, on the other hand, are smaller and lack both cartilage and submucosal glands. Their walls are supported mainly by smooth muscle, and mucus production is minimal, with the epithelium changing to cells like club cells further down. This structural shift—from cartilage and glands in the bronchi to their absence in the bronchioles—explains why bronchioles are more flexible and more subject to constriction, while bronchi are rigid and mucus-secreting.