How are the alveoli designed to maximise the exchange of gases?

The alveoli are designed to maximize the exchange of gases in several ways:

1. Large Surface Area: The human lungs contain about 300-500 million alveoli, providing a large surface area (about 75 m2) for gas exchange.

2. Thin Walls: The walls of the alveoli are extremely thin (about 0.2 micrometers), which allows gases to easily diffuse across them.

3. Rich Blood Supply: The alveoli are surrounded by a dense network of capillaries, which carry oxygen-poor blood from the heart to the lungs, and oxygen-rich blood from the lungs back to the heart. This ensures a constant supply of oxygen and carbon dioxide for gas exchange.

4. Moist Lining: The alveoli are lined with a thin layer of fluid, which helps to dissolve the gases and facilitates their diffusion across the alveolar and capillary walls.

5. Good Ventilation: The regular inflow and outflow of air in the lungs (ventilation) ensures that the concentration gradients of oxygen and carbon dioxide between the alveoli and the blood are maintained, which is necessary for efficient gas exchange.