Chorionic villi are microscopic and fingerlike projections found near the placenta which contain capillaries, increase surface area of blood that allow blood to flow and transfer nutrients from the mother to the fetus. The chorionic villi is adjacent to the yolk sac because it developed from the yolk sac, villi can extend and contact maternal blood vessels thereby nourishing the embryo and transfering nutrients from the mother to the fetus.
ABC transporters are transmembrane proteins that enable active transportation of substances across the cell membrane. The protein is important in the movement of substances against their concentration gradient using ATP energy. ATP binding causes it to change conformation and bind the molecule being transported.
