What adaptations make the alveoli effective for gas exchange?

The alveoli are effective for gas exchange due to their large surface area, thin walls, and rich blood supply.

The alveoli, tiny air sacs in the lungs, are specialised for gas exchange. One of the key adaptations that make them effective is their large surface area. There are millions of alveoli in each lung, and this vast number increases the surface area available for gas exchange. This means that a large amount of oxygen can be absorbed into the bloodstream, and a large amount of carbon dioxide can be expelled from the body, at any one time.

Another important adaptation is the thinness of the alveolar walls. These walls are only one cell thick, which allows gases to easily diffuse across them. This is crucial for efficient gas exchange, as it reduces the distance that gases have to travel to reach the bloodstream. The thin walls also mean that the alveoli are very delicate, and they are surrounded by a network of tiny blood vessels, or capillaries, to protect them.

The alveoli also have a rich blood supply, which is another key adaptation for gas exchange. The capillaries that surround the alveoli carry deoxygenated blood from the heart to the lungs, where it picks up oxygen and releases carbon dioxide. This blood is then returned to the heart, where it is pumped around the body to deliver oxygen to the cells. The rich blood supply ensures that there is always a high concentration of oxygen in the alveoli, and a low concentration of carbon dioxide, which maintains the concentration gradient necessary for diffusion.

Finally, the alveoli are coated with a thin layer of moisture, which helps to dissolve the gases and facilitates their diffusion across the alveolar walls. This is another important adaptation that enhances the efficiency of gas exchange in the lungs.