Question:hard
Which of the following statements regarding fetal circulation is correct?
Which of the following statements regarding fetal circulation is correct?
Show Hint
HbF shifts the curve left and the foramen ovale stays open until birth.
Updated On: Jun 24, 2026
- The liver and heart of the fetus receive blood with very high oxygen saturation
- PO2 of fetal blood leaving the placenta is slightly greater than maternal mixed venous PO2
- The presence of fetal hemoglobin shifts the oxyhemoglobin dissociation to the right
- The foramen ovale closes during the third trimester unless the fetus has an atrial septal defect
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Trace the oxygen path. Blood enriched at the placenta travels up the umbilical vein, supplies the liver, and is carried by the ductus venosus into the IVC. Streaming directs this oxygen rich blood across the foramen ovale to the left heart, so coronary and cerebral vessels, along with the liver, get the richest blood. That validates choice (a).
Step 2: Evaluate the placental PO2 claim. The placenta is a relatively poor oxygen exchanger, and umbilical venous PO2 sits near 30 mm Hg, below the mother's mixed venous value. So saying fetal blood leaving the placenta exceeds maternal venous PO2 is false, ruling out (b).
Step 3: Consider HbF. Its reduced binding of 2,3-BPG raises oxygen affinity and displaces the dissociation curve leftward, the opposite of choice (c), which therefore fails.
Step 4: Finally the foramen ovale. It is a physiological right to left shunt that persists in utero and seals after delivery as pulmonary flow and left atrial pressure climb, so closing in the third trimester (d) is incorrect. Only statement (a) holds.
\[\boxed{\text{Liver and heart receive blood with very high oxygen saturation}}\]
Step 2: Evaluate the placental PO2 claim. The placenta is a relatively poor oxygen exchanger, and umbilical venous PO2 sits near 30 mm Hg, below the mother's mixed venous value. So saying fetal blood leaving the placenta exceeds maternal venous PO2 is false, ruling out (b).
Step 3: Consider HbF. Its reduced binding of 2,3-BPG raises oxygen affinity and displaces the dissociation curve leftward, the opposite of choice (c), which therefore fails.
Step 4: Finally the foramen ovale. It is a physiological right to left shunt that persists in utero and seals after delivery as pulmonary flow and left atrial pressure climb, so closing in the third trimester (d) is incorrect. Only statement (a) holds.
\[\boxed{\text{Liver and heart receive blood with very high oxygen saturation}}\]
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