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Where does gas exchange take place in the human lungs?

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Medical illustration of the human chest showing the lungs, diaphragm, ribs, trachea, bronchus, and bronchioles, with one lung cut away to reveal internal structures. — human respiratory system The lungs serve as the gas-exchanging organ for the process of respiration.

In the human lungs, gas exchange takes place in the alveoli, which are small, pocketlike air sacs located at the ends of the bronchioles.12

These structures are organized into clusters called alveolar sacs and are surrounded by a dense network of pulmonary capillaries. The exchange of oxygen and carbon dioxide occurs across the extremely thin membranous barrier—approximately 0.5 μm thick—that separates the air in the alveoli from the blood in the capillaries.12

This process is driven by diffusion, where gases move from areas of higher partial pressure to areas of lower partial pressure. The parenchyma, or the essential gas-exchanging tissue of the lung, provides an immense internal surface area, estimated at 50 to 100 square metres in adults, which facilitates the efficient transfer of these respiratory gases.123