Physiology, Fetal Hemoglobin

Excerpt

Fetal hemoglobin (HbF) is the dominant form of hemoglobin present in the fetus during gestation. HbF is produced by erythroid precursor cells from 10 to 12 weeks of pregnancy through the first six months of postnatal life. HbF contains two alpha and two gamma subunits, while the major form of adult hemoglobin, hemoglobin A (HbA), contains two alpha and two beta subunits. The genes that express gamma chain proteins are present in the beta chain locus on chromosome 11. The gamma subunit differs from its adult counterpart in that it contains either an alanine or a glycine at position 136, both of which are neutral, nonpolar amino acids. This difference introduces conformational changes to the protein that gives rise to several physiological differences in oxygen delivery that are important in fetal circulation.