Which of the following is a true statement?
A - Oxygen diffuses from the maternal blood in the intervillous space, through trophoblasts in the chorionic villi, and into the fetal bloodstream.
B - Waste products from the fetus diffuse out of capillaries in the chorionic villi and into the umbilical vein, which carries them back to the mother who will be able to remove them from her blood.
C - Maternal blood is supplied to the fetus through the umbilical cord.
D - Nutrients diffuse from the maternal blood in the umbilical cord, through trophoblasts in the chorionic villi, and into the fetal bloodstream.
Answer: A
Maternal blood flows from the mother's circulatory system, through the intervillous space and then re-enters the mother's blood vessels. Fetal blood flows from the fetus into two main arteries in the umbilical cord, through the capillary network of the chorionic villi and is returned to the fetus by the umbilical vein. The maternal blood that enters the placenta is nutrient and oxygen rich.