The organ primarily responsible for oxygen exchange in the body is the lungs. Located in the thoracic cavity, the lungs are crucial components of the respiratory system. They function to take in oxygen from the atmosphere when we inhale and expel carbon dioxide, a waste product of metabolism, when we exhale. The alveoli, tiny air sacs within the lungs, are where the exchange of gases occurs. Oxygen diffuses from the air in the alveoli into the bloodstream, while carbon dioxide moves from the blood to the alveoli to be expelled.