Describe and explain how the alveoli are adapted to facilitate effective gas exchange in the lungs.

The alveoli have a number of adaptations for effective gaseous exchange. Firstly, they have a very large surface area to volume ratio; the combined surface area of the alveoli is approximately 50-75m² - larger than the floor area of a 4 bedroom house! This large surface area allows faster diffusion which is important as we need lots of oxygen! They also utilise a short diffusion distance; the walls of the alveoli and the capillaries that surround them are only one cell thick. This means that the gases do not have to travel far from the air to the blood, increasing the speed of gas exchange. The alveoli have an excellent blood supply bringing a constant supply of deoxygenated blood. This maintains a steep concentration gradient for both carbon dioxide in the blood and oxygen in the air.Finally, the act of breathing maintains the concentration gradient of gases in the lungs. This is aided by the elastic recoil of the alveoli as they stretch as air is draw in before recoiling and forcing the air out.