Describe the adaptations for efficient gas exchange in the lungs?

For efficient diffusion there must be a concentration gradient that is maintained, a large surface area to volume ration and a short distance for the gases to diffuse across. There are adaptations at the site of gas exchange in the lungs that allow the diffusion of oxygen into the blood stream and the diffusion of waste gases out of the blood so that they can be expired.There are many alveoli sacs which create a large surface area to volume ratio and many blood capillaries- increasing the surface area available for the diffusion of gases. The blood is constantly moving through the capillaries which helps to maintain the concentration gradient required for diffusion of gases from a high concentration to a low concentration. The distance for diffusion is kept minimal as the capillary walls are one cell thick, as are the walls of the alveoli. This distance is further reduced by the fact that the red blood cells squished against the walls of the capillaries.