Final answer:
The largest umbilical vein carries oxygen- and nutrient-rich blood to the fetal heart, while the two smaller umbilical arteries carry oxygen-depleted blood to the placenta for waste removal.
Step-by-step explanation:
The largest umbilical vein carries oxygen- and nutrient-rich blood from the placenta to the fetal heart. It is important for supplying the fetus with the necessary oxygen and nutrients for growth and development.
The two smaller openings, which are the umbilical arteries, carry oxygen-depleted blood from the fetus to the placenta. These arteries are responsible for removing waste and carbon dioxide from the fetal circulation.