What structure is responsible for the exchange of gases in the lungs?

The alveoli are the structures in the lungs that are primarily responsible for the exchange of gases, specifically oxygen and carbon dioxide. These tiny, balloon-like sacs are located at the end of the respiratory tree, branching off from the bronchioles. Each alveolus is surrounded by a network of capillaries, which are small blood vessels, creating a large surface area for gas exchange to occur.

When air enters the lungs, oxygen moves from the alveoli into the blood in the capillaries, while carbon dioxide moves from the blood into the alveoli to be exhaled. The thin walls of the alveoli facilitate this efficient exchange, allowing for a rapid transfer of gases based on the principles of diffusion.

In contrast, structures like the bronchi and bronchioles are involved in the conduction of air, transporting it into the alveoli but not participating directly in gas exchange. The pleura, which are membranes surrounding the lungs, are also not involved in gas exchange but serve to protect the lungs and reduce friction during breathing. Thus, the alveoli are pivotal for respiration, making them the correct answer.