The alveoli are surrounded by a dense network of capillaries, which ensures that the blood is constantly being exposed to the gases.
Diffusion is the process by which gases move from an area of high concentration to an area of low concentration. This is how oxygen moves from the alveoli to the blood, and carbon dioxide moves from the blood to the alveoli.
The rate of diffusion is affected by a number of factors, including the concentration gradient, the surface area, the distance between the two areas, and the temperature.
The alveoli are adapted for gas exchange because they maximize all of these factors. The concentration gradient between the alveoli and the blood is very high, the surface area of the alveoli is very large, the distance between the alveoli and the blood is very small, and the temperature inside the lungs is relatively high.
In addition to the features listed above, the alveoli also have a number of other adaptations that help to improve gas exchange, including:
Surfactant: The alveoli are lined with a substance called surfactant, which helps to keep the alveoli open and prevents them from collapsing.
Elastic fibers: The alveoli contain elastic fibers, which help them to recoil after they have been inflated. This helps to keep the alveoli open and allows them to exchange gases efficiently.
Blood vessels: The blood vessels that supply the alveoli are very efficient at transporting gases. The walls of the blood vessels are very thin, which allows for rapid diffusion of gases.
The alveoli are highly adapted for gas exchange. Their thin walls, moist walls, large surface area, and rich blood supply all help to maximize the rate of diffusion of gases. The alveoli also have a number of other adaptations, such as surfactants, elastic fibers, and efficient blood vessels, which help to improve gas exchange.
