So this is what takes place within that fetal circulatory system. Now, what happens as soon as that individual, as soon as that fetus is born? What happens during the first breath? Well, remember, the alveoli of the lungs are completely filled with the fluid. But as soon as the first breath takes place, all that air that rushes into the alveoli of that lung displaces and removes pushes all that fluid out of the alveoli. And this expands the alveoli.