Gas exchange in the lungs allows oxygen to diffuse through the small air sacks or alveoli at the end of one's bronchial tubes into the blood, and it allows carbon dioxide to move from the blood into the alveoli to allow the individual to expel the waste. Fresh oxygen comes into the lungs when one inhales and is removed upon exhaling, according to WebMD.
A healthy human inhales six to 10 liters of air per minute, with 0.3 liters of oxygen transferred to the blood per minute. As oxygen molecules attach to the red blood cells, a similar amount of carbon dioxide releases from the blood into the alveoli.
The tissue separating air from the blood averages 1 micron in thickness. In most locations, only one cell separates the two. This allows rapid gas exchange to occur. Once oxygenated, blood is transported through pulmonary veins to the heart, where it is then pumped to the rest of the body. Inside the body, the oxygenated blood provides oxygen to cells, and it removes carbon dioxide. The deoxygenated blood returns to the right side of the heart where it is forced to the lungs again in order to begin the gas exchange that creates oxygen-rich blood again.