Which structures are part of the lower respiratory system?

• A. Nasal cavity and pharynx
• B. Trachea, primary bronchi, lungs
• C. Larynx and epiglottis
• D. Alveoli and capillaries

Answer: (B)

The lower respiratory system includes structures that are involved in the exchange of gases and further conduction of air deeper into the lungs. The trachea, primary bronchi, and lungs are integral components of this system.

The trachea, often referred to as the windpipe, conducts air from the larynx down into the bronchi. The primary bronchi branch off the trachea to direct air into the left and right lungs. The lungs contain intricate structures such as the bronchioles and alveoli, where the actual gas exchange occurs—oxygen is absorbed into the blood, and carbon dioxide is expelled.

Other options include structures that are either part of the upper respiratory system or not directly involved in gas exchange. For example, the nasal cavity and pharynx are located in the upper respiratory tract and are primarily involved in filtering, humidifying, and warming the air before it enters the lower structures. The larynx and epiglottis play essential roles in protecting the airway and enabling sound production but are not considered part of the lower respiratory system. Although alveoli are crucial for gas exchange, pairing them with capillaries does not define a complete system like the trachea, bronchi, and lungs do. Thus,