The substance that is being released during the exchange of air in your lungs is carbon dioxide (CO2). As you inhale, oxygen (O2) diffuses from the alveoli (tiny air sacs in the lungs) into the bloodstream, where it binds with hemoglobin in red blood cells and is transported to your body's cells. At the same time, carbon dioxide, which is a waste product produced by your body's cells, diffuses from the bloodstream into the alveoli and is exhaled when you breathe out. This process is known as gas exchange or respiration.
