CHAPTER 34Circulation Through Special Regions 583have a greater O 2 affinity than adult red cells (Figure 34–19).
The fetal red cells contain fetal hemoglobin (hemoglobin F),
whereas the adult cells contain adult hemoglobin (hemoglobin
A). The cause of the difference in O 2 affinity between the two
is that hemoglobin F binds 2, 3-DPG less effectively than he-
moglobin A does. The decrease in O 2 affinity due to the bind-
ing of 2, 3-DPG is discussed in Chapter 32).
Some hemoglobin A is present in blood during fetal life (see
Chapter 32). After birth, production of hemoglobin F nor-
mally ceases, and by the age of 4 mo 90% of the circulating
hemoglobin is hemoglobin A.FIGURE 34–17 Diagram of the circulation in
the fetus, the newborn infant, and the adult. DA,
ductus arteriosus; FO, foramen ovale. (Redrawn and
reproduced with permission from Born GVR et al: Changes in
the heart and lungs at birth. Cold Spring Harbor Symp Quant
Biol 1954;19:102.)PlacentaBodyL heartLungsR heartBodyL heartLungsR heartBodyL heartLungsR heartDA DAFOFETUS NEWBORN ADULTFIGURE 34–18 Circulation in the fetus. Most of the oxygenat-
ed blood reaching the heart via the umbilical vein and inferior vena
cava is diverted through the foramen ovale and pumped out the aorta
to the head, while the deoxygenated blood returned via the superior
vena cava is mostly pumped through the pulmonary artery and ductus
arteriosus to the feet and the umbilical arteries.
Pulmonary
arteryLeft atriumLeft
ventricleAortaUmbilical
arteriesPortal
vein
Umbilical
veinSuperior vena
cavaForamen
ovaleRight atriumRight ventricleDuctus
arteriosusDuctus venosusFrom
placentaInferior
vena cavaTo placentaFIGURE 34–19 Dissociation curves of hemoglobin in human
maternal and fetal blood.22
20
18
16
14
12
10
8
6
4
2
0
10 20 30 40 50 60 70 80 90100
PO 2 (mm Hg)Ocontent (mL/dL) 2FetusMother