How is the placenta adapted for diffusion?

At placenta, you have a membranes from mother and fetus come in close contact. The area of contact is fairly large, much more than you can imagine. Here the blood from mother and the fetus come in close contact, but does not get mixed up. Through this so called placental barrier, only very small molecules can pass. So all the amine acids, glucose, fat molecules ( may be fatty acids and glycerol) vitamins and minerals along with water can pass through this membrane. Globulin can pass but not albumin. That is the beauty of Nature.