Compared with adult hemoglobin, fetal hemoglobin has a left-shifted dissociation curve, which means what about oxygen affinity?

Compared with adult hemoglobin, fetal hemoglobin has a left-shifted dissociation curve, which means what about oxygen affinity?

• A. Higher affinity
• B. Lower affinity
• C. No change in affinity
• D. Variable affinity

Answer: (A)

A left shift in the oxygen-hemoglobin dissociation curve means hemoglobin binds oxygen more readily and holds onto it more tightly, indicating higher oxygen affinity. Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin because its gamma chains and reduced 2,3-BPG binding shift its curve to the left. This allows the fetus to extract oxygen efficiently from maternal blood in the placenta, where the partial pressure of oxygen is relatively low. At the same oxygen partial pressures, fetal hemoglobin is more saturated than adult hemoglobin. So the correct interpretation is increased oxygen affinity. Lower affinity would correspond to a rightward shift, no change would mean the same curve, and variable affinity isn’t described by a left-shift pattern.

A left shift in the oxygen-hemoglobin dissociation curve means hemoglobin binds oxygen more readily and holds onto it more tightly, indicating higher oxygen affinity. Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin because its gamma chains and reduced 2,3-BPG binding shift its curve to the left. This allows the fetus to extract oxygen efficiently from maternal blood in the placenta, where the partial pressure of oxygen is relatively low. At the same oxygen partial pressures, fetal hemoglobin is more saturated than adult hemoglobin. So the correct interpretation is increased oxygen affinity.

Lower affinity would correspond to a rightward shift, no change would mean the same curve, and variable affinity isn’t described by a left-shift pattern.