And that's important because the lungs do need a small amount of oxygen to keep on developing so that at birth, those lungs can actually function properly and efficiently. So these are the two lungs that are used by the circulatory system of that fetus to basically redirect blood away from the lungs. Now, what happens at birth? Well, as soon as that fetus is bored and takes their first breath, what happens is the air rushes into the alveoli of the lungs and it displaces the fluid that is within the alveoli of the lungs. And that decreases. It drops the resistance and pressure inside those lungs.