Explain how the alveoli create a surface for efficient gaseous exchange

Firstly, the alveoli walls consist of a one-cell thick layer of squamous epithelium. This means there is a thin barrier to diffusion, and a small distance for oxygen molecules to diffuse across to get to blood in the alveolar capillaries. The alveoli are elastic, so are able to recoil during exhalation, forcing air out of the lungs. During breathing, oxygen flows down its concentration gradient from the alveolar space to the blood - this gradient is maintained by the alveoli. The small size and huge number of alveoli also provide a massive surface area to volume ratio for gaseous exchange to occur across. This surface area is maintained by surfactant, which is secreted by type I alveolar cells.