Fetal to Neonatal Circulation Transition

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  2. In the fetal circulation, the right and left ventricles exist in a parallel circuit, as opposed to the series circuit of a newborn or adult.

  3. Three cardiovascular structures unique to the fetus are important for maintaining this parallel circulation:

    1. The ductus venosus
    2. Foramen ovale
    3. Ductus arteriosus

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  5. In the fetus, the placenta is the organ of respiration not lungs.

  6. Because the lungs do not provide gas exchange, the pulmonary vessels are vasoconstricted, diverting blood away from the pulmonary circulation.

  7. However, placenta is not as efficient an oxygen-exchange organ as the lungs, so that umbilical venous PO2 is low.

  8. Because the pulmonary arterial circulation is vasoconstricted, only approximately 5% of right ventricular (RV) outflow enters the lungs.

  9. RV is not only pumping against systemic blood pressure, but also performing a slightly greater volume of work than the left ventricle. Thus the RV wall is as thick as the LV wall during fetal and immediate neonatal life.

  10. Fetal Circulation:

    1. 50%

      50%

      Eustachian Valve

      via Tricuspid Valve

      5%

      95%

      35%

      65%

      Placenta (oxygenated blood)

      Umbilical Vein (low PO2)

      Hepatic Circulation

      Ductus Venosus

      IVC

      Right Atrium

      Foramen Ovale

      Left Atrium

      Left Ventricle

      Ascending Aorta

      Brain & Upper Body

      SVC (Low PO2)

      Right Ventricle

      Pulmonary Artery

      Lungs

      Ductus Arteriosus

      Descending Aorta

      Common Iliac Artery

      Internal Iliac Artery

      Umbilical Arteries

      Lower Body

      Back to Placenta

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Fetal to Neonatal Circulation Transition