how are Alveoli designed to maximize the exchange of gases ?

 The alveoli are the small balloon-like structures present in the lungs. The walls of the alveoli consist of extensive network of blood vessels. Each lung contains 300−350 million alveoli, making it a total of approximately 700 million in both the lungs. The alveolar surface when spread out covers about 80 m² area. This large surface area makes the gaseous exchange more efficient.

^{_{Alveoli provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO2 from the blood brought from the body, diffuses out into the air.}}

The alveoli (microscopic air sacs) in the lungs are adapted to maximizegas exchange- the membrane is thin and the blood capillaries are close to the membrane, so the distance for diffusion of gases is very small. There is also a large amount ofcarbon dioxidein the bloodaround the alveoli and a large amount of oxygen inside the alveolus, so the concentration gradient encourages oxygen to diffuse in and the carbon dioxide to diffuse out. There are also millions of alveoli in the lungs, which gives the lungs a large surface area for diffusion and a large capacity for air.