Ii

Inferior vena cava

Ductus venosus

Sphincter in ductus venosus

Pulmonary vein

Inferior vena cava

Pulmonary vein

Ductus venosus

Sphincter in ductus venosus

Inferior vena cava

Blood Flow Before Birth

Pulmonary artery

'-Descending aorta

Umbilical arteries

Figure 11.47 Fetal circulation before birth. Arrows, direction of blood flow. Note where oxygenated blood mixes with deoxygenated blood: in the liver (I), in the inferior vena cava (II ), in the right atrium (III ), in the left atrium (IV), and at the entrance of the ductus arteriosus into the descending aorta (V).

Pulmonary artery

'-Descending aorta

Umbilical arteries

Figure 11.47 Fetal circulation before birth. Arrows, direction of blood flow. Note where oxygenated blood mixes with deoxygenated blood: in the liver (I), in the inferior vena cava (II ), in the right atrium (III ), in the left atrium (IV), and at the entrance of the ductus arteriosus into the descending aorta (V).

pulmonary vessels is high, such that most of this blood passes directly through the ductus arteriosus into the descending aorta, where it mixes with blood from the proximal aorta. After coursing through the descending aorta, blood flows toward the placenta by way of the two umbilical arteries. The oxygen saturation in the umbilical arteries is approximately 58%.

During its course from the placenta to the organs of the fetus, blood in the umbilical vein gradually loses its high oxygen content as it mixes with desaturated blood. Theoretically, mixing may occur in the following places (Fig. 11.47, I-V): in the liver (I), by mixture with a small amount of blood returning from the portal system; in the inferior vena cava (II), which carries deoxygenated blood returning from the lower extremities, pelvis, and kidneys; in the right atrium (III), by mixture with blood returning from the head and limbs; in the left atrium (IV), by mixture with blood returning from the lungs; and at the entrance of the ductus arteriosus into the descending aorta (V ).

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Responses

  • jake
    Where is the inferior vena cava?
    8 years ago

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