Here's why:

* Alveoli: These are tiny air sacs in the lungs that are surrounded by capillaries (tiny blood vessels).

* Gas Exchange: Oxygen from the inhaled air diffuses across the thin walls of the alveoli and into the capillaries, where it enters the bloodstream. At the same time, carbon dioxide from the blood diffuses into the alveoli and is exhaled.

* Nutrient Exchange: While the primary function of the alveoli is gas exchange, nutrients are also transported via the bloodstream. The capillaries surrounding the alveoli allow for the exchange of nutrients, such as glucose, amino acids, and fatty acids, from the blood to the lung tissue.

Let me know if you'd like to know more about the process of gas exchange or nutrient exchange!