Which structure is part of the lower respiratory tract?

• A. Bronchioles
• B. Nasal cavity
• C. Pharynx
• D. Larynx

Answer: (A)

Distinguishing where airways are located helps you tell upper from lower parts of the respiratory system. The bronchioles are small airways that lie inside the lungs, branching off from the bronchi and continuing toward the alveoli. They are part of the lower respiratory tract, located within the thoracic cavity, and their structure includes smooth muscle with little to no cartilage, which is why they’re key in regulating airflow within the lungs.

In contrast, the nasal cavity, pharynx, and larynx are located above the thoracic inlet and form the upper airway. They mainly handle air preparation (warming, humidifying, filtering) and, in the case of the larynx, voice production. So the structure that fits the lower respiratory tract is the bronchioles.