Within the pool of maternal blood we have oxygen. And oxygen moves down its concentration gradient from the pool of blood and into the capillaries of that fetus. At the same time, carbon dioxide is deposited out of the capillaries of that fetus and into the pool of blood and eventually picked up by the maternal blood veins. And that carries the carbon dioxide to the lungs of that mother and the lungs expel the carbon dioxide to the rest of that environment. At the same time, when the lungs inhale, they bring in oxygen. And that oxygen is ultimately brought into this pooling area of that maternal blood.