Which structure is the site of gas exchange in the lungs?

The alveoli are the structures in the lungs that facilitate gas exchange. They are small, balloon-like air sacs situated at the end of the bronchioles and are surrounded by a network of capillaries. The walls of the alveoli are extremely thin, allowing oxygen to diffuse into the blood and carbon dioxide to diffuse out. This process is essential for respiration, as it allows the body to take in oxygen needed for cellular processes and remove the waste product, carbon dioxide.

In contrast, the bronchi are larger air passages that lead from the trachea to the lungs and are responsible for directing airflow but do not exchange gases themselves. The trachea is the windpipe that connects the throat to the bronchi and serves as a conduit for air to reach the lungs but also does not partake in gas exchange. The pleura are membranes that surround the lungs, providing lubrication to facilitate movement during breathing but they do not play a direct role in gas exchange either. Hence, the alveoli are uniquely designed and perfectly structured for the critical function of gas exchange in the respiratory system.