The Fetal Circulation:
The linked diagram will greatly enhance your understanding of the fetal circulation - study it carefully (Figure 2.13)!
Forty-six units of blood flow to the placenta via the umbilical artery, and 46 units return to the fetus via the umbilical vein. While in the placenta, this blood flowing through fetal villi, were bathed in a pool of maternal blood. Although there was no actual contact between the two bloods, oxygen diffused in and C02 diffused out.
Half of the umbilical vein blood passes through the portal circulation of the liver, half is shunted through the ductus venosus directly to the inferior vena cava. Admixtures of less oxygenated venous blood are added to the liver flow from vessels of the abdominal viscera, and to the inferior vena caval blood from vessels of the thigh, kidney, thoracic and abdominal walls. Thus the total flow returning to the heart via the inferior vena cava is 70 units.
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