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The Placenta Quiz
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Which blood vessel carries oxygenated blood from the placenta to the foetus?
- A Umbilical artery You picked ✕
- B Umbilical vein You picked ✓
- C Vitelline vein You picked ✕
- D Ductus arteriosus You picked ✕
- E Ductus venosus You picked ✕
Correct!
Incorrect
The answer is B: Umbilical vein
Explanation
Why B is correct
See Blood Vessels. Option B is correct. Blood vessels are named by the direction of flow relative to the heart, not by how much oxygen they carry. An artery carries blood away from the heart and a vein carries blood towards it. In the foetus the single umbilical vein runs from the placenta towards the foetal heart, so it is a vein, even though it carries oxygen-rich blood. It also brings nutrients. The two umbilical arteries run the other way, from the foetus to the placenta, carrying deoxygenated blood and waste products to be cleared. The usual rule of thumb that arteries carry oxygenated blood does not hold here, which is why the naming is a classic exam trap. The foetus does not breathe air or digest food, so everything it needs arrives through the placenta, where the villi (finger-like projections that increase the surface area for exchange) lie in pools of maternal blood.
- Naming rule: arteries carry blood away from the heart and veins carry it towards it.
- Umbilical vein: a single vessel carrying oxygen-rich blood from the placenta to the foetus.
- Umbilical arteries: two vessels carrying deoxygenated blood and waste from the foetus to the placenta.
Why the other options are incorrect
- A. Umbilical artery: The umbilical artery carries deoxygenated blood and waste from the foetus to the placenta, because it runs away from the foetal heart. It is the opposite direction to the vessel that is asked for. Your answer
- C. Vitelline vein: Vitelline veins drain the yolk sac in the early embryo, not the placenta. They are not the vessel that carries oxygenated blood from the placenta to the foetus, so this cannot be correct. Your answer
- D. Ductus arteriosus: The ductus arteriosus shunts blood from the pulmonary artery to the aorta, bypassing the lungs. It carries deoxygenated blood from the right side of the foetal circulation rather than oxygenated blood from the placenta. Your answer
- E. Ductus venosus: The ductus venosus is a shunt that carries oxygenated blood from the umbilical vein to the inferior vena cava, bypassing the liver. It lies within the foetus, so it does not bring blood from the placenta; that is the role of the umbilical vein. Your answer
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