Why are the lungs adapted for the rapid absorption of oxygen into the blood?

Oxygen is absorped into the blood by the process of diffusion. A large surface area, short diffusion pathway (the distance the oxygen has to travel through) and large concentration gradient increases the rate of diffusion and therefore oxygen absorption. The lungs are made up of many tiny air sacs called alveoli. These provide a large surface area due to their curved shape. They have very thin walls which means the diffusion pathway is short. The lungs also have a good blood supply as they contain many capillaries. This maintains a large concentration gradient.