Which of the following respiratory processes occurs primarily in the alveoli?

• A. Ventilation
• B. Diffusion of gases
• C. Filtration of air
• D. Conduction of air

Answer: (B)

The process that occurs primarily in the alveoli is the diffusion of gases. The alveoli are tiny air sacs located at the end of the respiratory bronchioles, and they are the primary site for gas exchange in the lungs. When air reaches the alveoli, oxygen from the air diffuses across the alveolar membrane into the bloodstream, while carbon dioxide from the blood diffuses into the alveoli to be exhaled. This exchange is driven by differences in partial pressures of the gases, a fundamental principle of gas movement.

Ventilation, on the other hand, refers to the movement of air into and out of the lungs and involves the bulk flow of air rather than molecular exchange of gases. Filtration of air occurs in the upper respiratory tract, primarily in the nasal passages and bronchi, where particles and pathogens are filtered out before air reaches the alveoli. Conduction of air pertains to the process of moving air through the airways (like trachea and bronchi) to the alveoli, but does not involve the exchange of gases. Therefore, diffusion of gases is specifically associated with the function of alveoli in gas exchange, making it the correct choice.