Final answer:
The function of the lower airway in the respiratory system is to 4) exchange oxygen and carbon dioxide in the alveoli. The lower airway structures are essential for this because they form a blood-air barrier that allows gases to diffuse easily.
Step-by-step explanation:
The function of the lower airway in the respiratory system is to exchange oxygen and carbon dioxide. This gas exchange process happens in the alveoli, where oxygen from the inhaled air diffuses into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled. The lower airway, including structures such as the trachea, bronchi, bronchioles, and alveoli, is crucial for this exchange due to the large surface area and the presence of a blood-air barrier that facilitates simple diffusion of gases. While the function of warming, filtering, and humidifying air is primarily carried out by the upper respiratory tract, namely the nasal cavity, protecting the lungs from aspiration, and delivering oxygenated blood to the cells are also essential functions of the respiratory system as a whole. These activities ensure that the air reaching the alveoli is clean, warm, and moist, to optimize the efficiency of the gas exchange process.