How do alveoli facilitate efficient gas exchange?

Alveoli facilitate efficient gas exchange through their large surface area, thin walls, and rich blood supply.

Alveoli are tiny air sacs located at the end of the bronchial tubes in the lungs. They are the primary site of gas exchange in the respiratory system. The structure of the alveoli is specifically designed to maximise the efficiency of this process.

One of the key features of alveoli that facilitate efficient gas exchange is their large surface area. Each lung contains millions of alveoli, which collectively provide a surface area of around 70 square metres - roughly the size of a tennis court. This large surface area allows a greater amount of oxygen and carbon dioxide to be exchanged at any given time.

The walls of the alveoli are also extremely thin, typically just one cell thick. This short diffusion distance allows gases to move quickly between the air in the alveoli and the blood in the surrounding capillaries. Oxygen diffuses from the air in the alveoli, across the alveolar wall, and into the blood. At the same time, carbon dioxide diffuses from the blood, across the alveolar wall, and into the air in the alveoli to be exhaled.

Lastly, the alveoli are surrounded by a dense network of capillaries, which provide a rich blood supply. This ensures that there is always a high concentration of blood ready to pick up oxygen and offload carbon dioxide. The constant flow of blood maintains a concentration gradient, which drives the diffusion of gases and further enhances the efficiency of gas exchange.

In summary, the large surface area, thin walls, and rich blood supply of the alveoli work together to facilitate efficient gas exchange, ensuring that the body's cells receive the oxygen they need and are able to get rid of waste carbon dioxide.