So it's not always true that arteries carry oxygenated blood. So let's go to number four. In number four, we have the blood moves from these pulmonary arteries into smaller arteries and arterioles and eventually they move into the capillary system that is found in the lung. We have the right lung and we have the left lung. Now, within the lung, we have an exchange taking place. We basically bring oxygen into the blood and we expel our carbon dioxide from our blood into the outside environment.