Which part of the respiratory system is responsible for gas exchange at the alveolar level?

The alveoli are small, thin-walled air sacs located at the ends of the bronchioles in the lungs. They are specifically designed for the exchange of gases between the air and the bloodstream. The alveolar walls are lined with a thin layer of cells that allows oxygen to pass into the blood and carbon dioxide to be expelled from the blood. This process is facilitated by the significant surface area provided by the numerous alveoli, which enables efficient diffusion.

In contrast, areas such as the bronchi, trachea, and bronchioles serve primarily as airway passages. The bronchi and trachea are large tubes that conduct air to and from the lungs, while the bronchioles are smaller branches leading to the alveolar sacs. Although these structures are essential for directing air into the lungs and facilitating ventilation, they do not perform gas exchange themselves. Hence, the primary responsibility for gas exchange resides within the alveoli.