Which structure in the lungs is responsible for gas exchange?

The alveoli are the tiny, sac-like structures located at the ends of the bronchial tubes in the lungs and play a crucial role in the respiratory system, specifically in gas exchange. Their thin walls allow for the effective diffusion of oxygen and carbon dioxide between the air in the alveoli and the blood in the surrounding capillaries. When we inhale, oxygen fills the alveoli, and it diffuses into the bloodstream, where it binds to hemoglobin in red blood cells. Conversely, carbon dioxide, which is a waste product from cellular metabolism, diffuses from the blood into the alveoli to be exhaled.

The other structures listed are important for other functions in the respiratory system. The bronchi serve as major air passages that lead from the trachea to the lungs, while the larynx is involved in sound production and protecting the trachea against food aspiration. The trachea is the windpipe that carries air to the bronchi but does not directly facilitate gas exchange. Thus, the uniqueness of the alveoli in enabling the exchange of gases makes them the critical structure for this vital process.