How does fetal hemoglobin differ from adult hemoglobin?

Fetal hemoglobin, known as hemoglobin F, has a distinct composition that allows it to bind oxygen with greater affinity compared to adult hemoglobin (hemoglobin A). This higher affinity is crucial for fetuses, as it enables efficient oxygen transfer from maternal blood to fetal blood within the placenta. The structural differences between fetal and adult hemoglobin contribute to this increased affinity; fetal hemoglobin contains two alpha and two gamma chains, whereas adult hemoglobin has two alpha and two beta chains. This composition changes the way oxygen molecules interact with hemoglobin, allowing fetal hemoglobin to pick up oxygen more readily in the lower oxygen environment of the placenta.

This unique adaptation is essential for fetal development, ensuring that the fetus receives adequate oxygen despite the lower partial pressures that it encounters compared to the maternal bloodstream. Therefore, the ability of fetal hemoglobin to bind oxygen more effectively is a critical physiological feature needed for survival and growth during gestation.