Similarly in the rest of the body, when we're going to the heart, where you're to see that that's de-oxygenated blood, but in the pulmonary vein, when we're going to the heart, it's oxygenated because the lungs are what take up the carbon dioxide and give us the oxygen. Now I still haven't answered that interesting question that rose on the message board on the last video. What happens to the 78% of nitrogen that's sitting here?