How does the oxygen dissociation curve for fetal hemoglobin compare to that for maternal hemoglobin?

• A. The fetal hemoglobin curve is identical to the maternal hemoglobin curve.
• B. The fetal hemoglobin curve is shifted downward, indicating a decreased oxygen capacity.
• C. The fetal hemoglobin curve is shifted to the right, indicating a lower affinity for oxygen.
• D. The fetal hemoglobin curve is shifted to the left, indicating a higher affinity for oxygen.

Answer: (D)

Verified step by step guidance

1. Understand the concept of the oxygen dissociation curve: It represents the relationship between the partial pressure of oxygen (x-axis) and the hemoglobin saturation with oxygen (y-axis).
2. Recognize the significance of the curve's position: A leftward shift indicates a higher affinity for oxygen, meaning hemoglobin binds oxygen more readily at lower partial pressures.
3. Identify the physiological differences between fetal and maternal hemoglobin: Fetal hemoglobin (HbF) has a different structure than adult hemoglobin (HbA), allowing it to bind oxygen more tightly.
4. Consider the biological necessity: The fetus relies on maternal blood supply for oxygen, so fetal hemoglobin must have a higher affinity to effectively extract oxygen from maternal blood.
5. Conclude that the fetal hemoglobin curve is shifted to the left compared to the maternal hemoglobin curve, indicating a higher affinity for oxygen, which is crucial for fetal oxygen uptake.