What gas is primarily exchanged in the alveoli?

The primary gas exchanged in the alveoli is oxygen. In the respiratory system, the alveoli are tiny air sacs located in the lungs where gas exchange occurs. When fresh air is inhaled, it flows into the alveoli, where oxygen from the air diffuses into the surrounding capillaries. This process takes advantage of the difference in concentration gradients; oxygen is present in higher concentrations in the alveoli compared to the blood in the capillaries, facilitating its movement into the bloodstream.

At the same time, carbon dioxide, a waste product of metabolism, diffuses from the blood into the alveoli to be exhaled. This exchange is vital for maintaining proper oxygen levels in the body and removing carbon dioxide, thereby supporting cellular respiration and overall metabolic processes.

The other gases listed do not play a primary role in the gas exchange process in the lungs. Nitrogen makes up a significant portion of the air we breathe but is largely inert and does not actively participate in gas exchange. Hydrogen is not a component of the respiratory process in this context and is not exchanged in the alveoli. Understanding the specific function of the alveoli in oxygen exchange is crucial for grasping respiratory physiology.