Which of the following statements are true of fetal hemoglobin?
I.Hemoglobin present in the fetus has a high affinity for oxygen.
II.HbF of normal-term infants has a P₅₀ of approximately 22 mm Hg.
III.A cyanotic newborn infant has a much lower arterial PO₂ than an equally cyanotic adult.
IV.By 6 months after birth, most HbF has been replaced with HbA.

Question

Quizplus · Accepted Answer

Hemoglobin present in the fetus has a high affinity for oxygen, apparently because 2,3-DPG does not bind with fetal hemoglobin (HbF). HbF and adult hemoglobin (HbA) without 2,3-DPG have similar left-shifted HbO₂ equilibrium curves. HbF of normal-term infants has a P₅₀of approximately 22 mm Hg. Thus, a cyanotic newborn infant has a much lower arterial PO₂ than an equally cyanotic adult. It is fortunate that HbF has a high affinity for oxygen because the maximum PO₂ of fetal blood is less than 40 mm Hg. Despite the low PO₂ HbF allows fetal blood to carry adequate amounts of oxygen. Because of its high affinity for oxygen, HbF vigorously takes up oxygen from the plasma at the placenta. This lowers fetal plasma PO₂ promoting oxygen trAnswerport across the placenta by maintaining an oxygen diffusion gradient. By 6 months after birth, most HbF has been replaced with HbA.

Which of the Following Statements Are True of Fetal Hemoglobin