MCAT Biology Question 45: Answer and Explanation

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Test Information

Question: 45

15. Which of the following statements regarding fetal circulation is FALSE?

  • A. In the umbilical cord, there are more arteries than veins.
  • B. The foramen ovale is the only shunt that connects two chambers of the heart.
  • C. Blood flow in the ductus arteriosus is from the aorta to the pulmonary artery.
  • D. The ductus venosus is the only shunt that bypasses the liver.

Correct Answer: C

Explanation:

Blood flow in the ductus arteriosus is from the pulmonary artery to the aorta. The direction of flow is determined by the pressure differential between the right side of the heart (and pulmonary circulation) vs. the left side of the heart (and systemic circulation). Unlike in adults, the right side of the heart is at a higher pressure during prenatal life than the left side, so blood will shunt from the pulmonary circulation to the systemic circulation through both the foramen ovale and ductus arteriosus.

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