What are alveoli primarily responsible for?

Alveoli are tiny air sacs located in the lungs and are primarily responsible for gas exchange. Their structure allows for a large surface area relative to their volume, which is critical for their function. When air enters the alveoli, oxygen from the air passes through the thin walls of the alveoli and into the surrounding capillaries where it binds to hemoglobin in red blood cells. At the same time, carbon dioxide, a waste product of metabolism, moves from the blood into the alveoli to be exhaled out of the body. This process is vital for maintaining proper oxygen levels in the blood and removing carbon dioxide, thus ensuring the body functions efficiently.

The other options focus on different body functions. Blood circulation is involved in transporting oxygen and nutrients throughout the body, but it is not the primary role of the alveoli. Transporting nutrients is a function of the digestive system and circulatory system rather than the respiratory system. Regulating body temperature is primarily managed through mechanisms in the skin and sweat glands rather than the alveoli. Thus, the role of alveoli is exclusively centered on facilitating effective gas exchange between the lungs and bloodstream.