The walls of alveoli very thin and surrounded by thin blood capillaries .It is in the alveoli that oxygen is taken into the body and CO2 is eliminated.It is known for gas exchange there are million of alveoli in the lungs

Structure of Alveoli:
Alveoli are tiny, balloon-like air sacs located at the end of bronchioles in the lungs. They are the site of gas exchange between the lungs and bloodstream. Alveoli have a unique structure that maximizes the exchange of gases.

Thin walls:
The walls of alveoli are very thin, just one cell thick, which allows for easy diffusion of gases. Oxygen from the air inhaled into the lungs can pass through the thin walls and enter the bloodstream. Similarly, carbon dioxide, a waste product of metabolism, can pass from the bloodstream into the alveoli and be exhaled out of the body.

High surface area:
The alveoli have a large surface area, which provides a greater area for gas exchange to occur. In fact, the surface area of the alveoli in the lungs is estimated to be about 70 square meters, which is roughly the size of a tennis court.

Moist environment:
The alveoli are coated with a thin layer of moisture, which helps to keep the walls moist and allows gases to dissolve easily. This helps to increase the efficiency of gas exchange.

Rich blood supply:
The alveoli have a rich blood supply, which helps to maintain a concentration gradient for gas exchange. Blood flowing through the capillaries surrounding the alveoli is constantly replenished with oxygen, while carbon dioxide is removed.

Elasticity:
The alveoli are highly elastic, which allows them to expand and contract as air moves in and out of the lungs during breathing. This helps to increase the efficiency of gas exchange by ensuring that all areas of the lungs are exposed to air.

Surfactant:
The alveoli are also lined with a substance called surfactant, which reduces the surface tension of the walls and prevents them from collapsing during exhalation. This helps to keep the alveoli open and allows for efficient gas exchange.

Conclusion:
In summary, the alveoli are designed to maximize the exchange of gases by having thin walls, a high surface area, a moist environment, a rich blood supply, elasticity, and surfactant. All of these factors work together to ensure that oxygen can be efficiently delivered to the bloodstream and carbon dioxide can be removed from the body.