Gas exchange in the lungs takes place primarily in the alveoli, which are tiny air sacs located at the ends of the bronchioles within the respiratory zone of the lungs

. The alveoli are surrounded by a dense network of capillaries, allowing oxygen to diffuse from the alveolar air into the blood and carbon dioxide to diffuse from the blood into the alveoli to be exhaled

. This gas exchange occurs across the respiratory membrane, which consists of the alveolar epithelium, the capillary endothelium, and their fused basement membranes. The thin walls of the alveoli and capillaries (only one cell thick) provide a very short diffusion distance, facilitating efficient gas transfer

. Key adaptations of the alveoli for gas exchange include:

• Large surface area due to millions of alveoli
• Thin walls to minimize diffusion distance
• Moist lining to allow gases to dissolve and diffuse
• Rich blood supply to maintain concentration gradients
• Good ventilation to supply fresh air continuously

In summary, gas exchange takes place in the alveoli of the lungs, where oxygen moves into the blood and carbon dioxide moves out, facilitated by the close proximity of alveoli and capillaries and the specialized structure of the respiratory membrane