How do the alveoli facilitate efficient gas exchange?

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

The 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. Their structure is specifically designed to maximise the efficiency of this process.

Firstly, the alveoli have a large surface area. Each lung contains millions of alveoli, and their combined surface area is approximately 70 square metres in an adult human. This large surface area allows for a greater amount of gas to be exchanged at any one time, increasing the efficiency of the process.

Secondly, the walls of the alveoli are extremely thin, usually only one cell thick. This short distance between the air in the alveoli and the blood in the capillaries allows gases to diffuse across quickly. Oxygen diffuses from the air in the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli, from where it can be exhaled.

Lastly, the alveoli are surrounded by a dense network of capillaries, which carry deoxygenated blood from the heart to the lungs. This rich blood supply ensures that there is always a high concentration of carbon dioxide in the blood arriving at the alveoli, and a low concentration of oxygen. This concentration gradient allows for efficient diffusion of gases.

In addition, the moist lining of the alveoli helps to dissolve gases, aiding their diffusion into and out of the blood. The alveoli also produce a substance called surfactant, which reduces the surface tension of the fluid lining the alveoli, preventing them from collapsing and ensuring that they remain open for gas exchange.

In summary, the alveoli facilitate efficient gas exchange through their large surface area, thin walls, and rich blood supply. Their moist lining and production of surfactant also play key roles in this process.