Where are alveoli located and what is their main function?

• A. In the lungs; they are the sites of gas exchange (oxygen in, carbon dioxide out)
• B. In the brain; they process signals
• C. In the liver; they produce bile
• D. In the heart; they pump blood

Answer: (A)

Alveoli are located in the lungs, at the ends of the tiny airways where gas exchange happens. Their walls are extremely thin and they’re surrounded by a dense network of capillaries, giving a large surface area for diffusion. This setup lets oxygen from the inhaled air move into the blood and carbon dioxide from the blood move into the alveolar air to be exhaled. In short, their main job is gas exchange between the air in the lungs and the bloodstream. The other options point to brain, liver, or heart functions, which involve signaling, bile production, and pumping blood, not gas exchange in the lungs.