1. Prepared by: Mrs. Mahdia Samaha Alkony
Fetal Circulation
Prepared by: Mrs. Mahdia Samaha Alkony

2. Anatomy and Physiology Fetal Circulation
Umbilical cord
2 umbilical arteries: return non-oxygenated blood, fecal waste, CO2 to placenta
1umbilical vein: brings oxygenated blood and nutrients to the fetus
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3. Anatomy and Physiology
Fetus depends on placenta to meet O2 needs while organs continue formation
Oxygenated blood flows from the placenta
To the fetus via the umbilical vein
After reaching fetus the blood flows through the inferior vena cava
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4. The differences between fetal and newborn circulation
The fetus received oxygen from the placenta and through the lungs after birth.
The fetal liver doesn’t have the metabolic function that it will have after birth because the mother performs these functions.
Three shunts are present in fetal life:
Ductus venosus: connects the umbilical vein to the inferior vena cava
Ductus arteriosus: connects the main pulmonary artery to the aorta
Foramen ovale: anatomic opening between the right and left atrium.
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5. Fetal Circulation
Blood travels from the inferior vena cava to the ductus venosis
Ductus Venosis
Small amount of blood routed to growing liver
Increased blood flow leads to large liver in newborns
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6. Fetal Circulation Blood continues to travel up the inferior vena cava
Empties into the right atrium of the heart
The blood then passes to the left atrium through the foramen ovale
Only about one-third of this blood reaches the lungs (due to high flow resistance since the lungs are not yet expanded, and due to hypoxic vasoconstriction
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7. A/P Fetal Circulation
Blood continues journey to the left ventricle blood is then pumped into the aorta
Blood is circulated to the upper extremities
Blood then returns to the right atrium
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8. A/P Fetal Circulation
From the right atrium, the blood goes to the right ventricle then to the pulmonary arteries
Pulmonary arteries
Small amount goes to the maturing lungs
Rest of blood is shunted away from lungs by ductous ateriosus back to aorta
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9. A/P Fetal Circulation
The placenta will re-supply the blood with oxygen
Fetal circulation is a low-pressure system
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10. As a result, the blood supplied to the lower half of the body has a relatively low O2 concentration(O2 saturation = 0.3).
The majority of this blood returns via the umbilical arteries to the placenta, where it is oxygenated again
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11. A/P Fetal Circulation Low pressure system Lungs are closed
Most oxygenated blood flows between the atria of the heart through the foramen ovale
This oxygen rich blood flows to the brain through the ductus arteriosus
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12. Mahdia Shaker

13. Conversion of Fetal to Infant Circulation
At birth
Clamping the cord shuts down low-pressure system
Increased atmospheric pressure(increased systemic vascular resistance) causes lungs to inflate with oxygen
Lungs now become a low-pressure system
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14. Conversion: Fetal to Infant Circulation
Pressure from increased blood flow in the left side of the heart causes the foramen ovale to close
More heavily oxygenated blood passing by the ductus arteriosus causes it constrict
Functional closure of the foramen ovale and ductus arteriosus occurs soon after birth
Overall anatomic changes are not complete for weeks
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15. What happens to these special structures after birth?
Umbilical arteries atrophy
Umbilical vein becomes part of the fibrous support ligament for the liver
The foramen ovale, ductus arteriosus, ductus venosus atrophy and become fibrous ligaments
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16. Human Fetal Circulation
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17. Overview of Conversion
Umbilical cord is clamped
Loose placenta
Closure of ductus venosus
Blood is transported to liver and portal system
Increased systemic resistance
Pressure in right atrium decreased
Change from right to left shunting to left to right blood flow
Increased O2 levels in pulmonary circulation
Closure of the ductus arteriosus
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18. Loss of placenta also leads to:
First breath
Lungs expand and fluid is expelled
Decreased pulmonary resistance
Increased pressure in left atrium
Closure of foramen ovale
Increased systemic resistance
Pressure in right atrium decreased
Change from right to left shunting to left to right blood flow
Increased O2 levels in pulmonary circulation
Closure of the ductus arteriosus
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19. Fetal vs. Infant Circulation
Low pressure system
Right to left shunting
Lungs non-functional
Increased pulmonary resistance
Decreased systemic resistance
Infant
High pressure system
Left to right blood flow
Lungs functional
Decreased pulmonary resistance
Increased systemic resistance

20. Shunts
Occur when the foramen ovale or ductus arteriosus remains open, placing a strain on the heart.
In patent foramen ovale (atrial septum defect), the blood flows from left atrium to right atrium (left-to-right shunt) lead to right ventricle (volume overload) , lungs and then left atrium.
In patent ductus arteriosus, the blood flows from aorta to pulmonary artery (= left-to-right shunt) leads to lungs (pressure overload) and then aorta.
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21. Flow Chart of Fetal Circulation
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