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In the alveoli, oxygen from the air is absorbed into the blood. Carbon dioxide, a waste product of metabolism, travels from the blood to the alveoli, where it can be exhaled. Between the alveoli is a thin layer of cells called the interstitium, which contains blood vessels and cells that help support the alveoli.
In summary, gas exchange is the movement of oxygen into the blood and carbon dioxide out of the blood across the respiratory membrane in the lungs. This respiratory surface, also known as the respiratory membrane, includes the alveolar epithelial cells as well as the pulmonary capillary endothelial cells.his large number of alveoli greatly increases the surface area for gas exchange. Now, the total surface area of alveoli is about 140 square meters or 1,500 square feet. Wow! That's about the size of a tennis court. So if you wonder why we have alveoli, well, now you know.