The primary role of the alveoli in the respiratory system is to facilitate gas exchange. These tiny air sacs, located in the lungs, provide a large surface area for oxygen to diffuse into the bloodstream and for carbon dioxide to be expelled from the blood. The alveoli's thin walls, combined with a rich supply of capillaries, enable efficient transfer of gases. This process is vital for maintaining adequate oxygen levels in the body and removing metabolic waste, supporting cellular respiration and overall bodily functions.