Final answer:
The umbilical vein carries oxygen and nutrients from the placenta directly to the fetus to support its development, as the fetal lungs are not functional for gas exchange (option c).
Step-by-step explanation:
The umbilical vein serves a vital function in prenatal circulation. Its main role is to carry oxygen-rich and nutrient-rich blood from the placenta to the fetus. This is essential because the fetal respiratory system is not yet mature enough to oxygenate blood on its own. Instead, the placenta acts as the site for gas and nutrient exchange between the mother and fetus. Oxygen and nutrients from the mother's blood diffuse into the placenta, then through the umbilical vein into the fetus's circulation, providing the necessary components for growth and development.
Once the oxygen-rich blood reaches the fetus via the umbilical vein, it flows toward the fetal heart through the inferior vena cava. This passage of blood is made possible through a shunt known as the ductus venosus, allowing the blood to largely bypass the immature liver directly to the heart. The blood enters the right atrium and is mixed with fetal venous blood before pumping through the body, ensuring all fetal tissues receive the oxygen and nutrients they need.
Correct Answer
The umbilical vein carries oxygen and nutrients from the placenta to the fetus (option c).