1-fetal circulation

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  • PO2 is 20mmHg


  • 1. SMS 1053 Dr. Mohanad R. Alwan
  • 2. 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
  • 3. The Placenta
    • The circulatory system of the mother is not directly connected to that of the fetus, so the placenta functions as the respiratory center for the fetus
    • as well as a site of filtration for plasma nutrients and wastes. Water, glucose, amino acids, vitamins, and inorganic salts freely diffuse across the placenta along with oxygen.
    • The uterine arteries carry oxygenated blood to the placenta, and permeates the sponge like material there.
  • 4. 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
    • Facilitates gas and nutrient exchange between maternal and fetal blood.The blood itself does not mix.
  • 5. Fetal Circulation
  • 6. How does the blood move??
    • Umbilical VEIN carries oxygenated blood and nutrients from the placenta to the fetus
    • Where does the vein enter??
        • At the navel and ascends into the liver
    • How is the blood dispersed??
      • ½ of the blood enters the liver while the other half comes into the ductus Venosus and then into the inferior vena cava
  • 7. Foramen Ovale
    • Blood is shunted from right atrium to left atrium, skipping the lungs.
    • More than one-third of blood takes this route.
    • Is a valve with two flaps that prevent back-flow.
  • 8. Fetal Circulation
    • Blood continues to travel from the inferior vena cava to the ductus Venosus
    • Ductus Venosus : shunts a significant majority (80%) of the blood flow of the umbilical vein directly to the inferior vena cava.
    • Ductus Venosus it allows oxygenated blood from the placenta to bypass the liver and puts blood into the hepatic veins.
      • Small amount of blood routed to growing liver
      • Increased blood flow leads to large liver in newborns
  • 9. What happens to the blood after it reaches the right atrium??
    • Blood flows right into the left atrium through the foramen ovale.
    • Alamak,What is that? It’s Small opening in the septum of the heart
    • Foramen ovale
      • Small opening in the septum of the heart
      • Completely by passes the non-functioning lungs
    • Here again it mixes with a smaller amount of deoxygenated blood from the pulmonary veins.
  • 10. F.C
    • Some of the blood entering the right atrium does not pass directly to the left atrium through the foramen ovale , but enters the right ventricle and is pumped into the pulmonary artery .
    • In the fetus, there is a special connection between the pu l monary artery and the aorta , called the ductus arteriosus , which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid)
  • 11. Ductus Arteriousus
  • 12. Fetal Circulation
    • After it proceeds to the left ventricle where it is pumped to the heart and brain
    • 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
  • 13.
  • 14. What about the rest of the blood??
    • The blood still in the right atrium goes into the right ventricle then to the pulmonary artery.
    • Once there most of the blood by passes the lungs and heads to the aorta through the ductus arteriosus.
    • About 15% of the blood flows through lungs to the right atrium by way of the pulmonary veins
    • Pulmonary arteries
      • Small amount goes to the maturing lungs
    • Rest of blood is shunted away from lungs by ductous ateriosus back to aorta
  • 15. What is happening further down??
    • Common iliac arteries branch into the external and internal iliacs.
    • The blood in the internal iliacs come into the umbilical arteries and flow back to the placenta to gather oxygen and to get rid of the waste products
    • Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, the maternal circulation
  • 16. 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
  • 17. What happens after birth?
    • Once the baby is born and the lung, renal, digestive and liver functions are working the fetal circulation undergoes some changes since they are no longer needed
  • 18. 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
      • Pressure from increased blood flow
  • 19. Conversion (cont)
    • 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
  • 20. Overview of Conversion
    • Umbilical cord is clamped
    • Loose placenta
    • Closure of ductus venosus
    • Blood is transported to liver and portal system
  • 21. Fetal vs. Infant Circulation
    • Fetal
    • 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
      • Overall anatomic changes are not complete for weeks