Where does oxygen exchange occur in the respiratory system?

Oxygen exchange occurs in the alveoli, which are tiny air sacs located at the end of the bronchioles in the lungs. The structure of the alveoli is critical to their function; they have thin walls and are surrounded by a network of capillaries. This design allows for efficient gas exchange through diffusion. When air enters the alveoli, oxygen from the air passes through the alveolar walls into the bloodstream in the capillaries, while carbon dioxide is transferred from the blood into the alveoli to be exhaled.

In contrast, other parts of the respiratory system, such as the bronchi, trachea, and nasal cavity, play different roles. The bronchi serve primarily as passageways for air to travel to the lungs but do not participate in gas exchange. The trachea acts as a windpipe, directing air from the larynx down to the bronchi, while the nasal cavity warms, humidifies, and filters the air before it enters the lungs. Thus, the alveoli are the only structures in the respiratory system directly involved in the exchange of oxygen and carbon dioxide.