Fetal circulation

• • Fetal blood circulation differs significantly from postnatal circulation due to the unique needs of the developing fetus. In the womb, the fetus relies on the placenta for oxygen and nutrient exchange rather than its own lungs and digestive system
• Components in fetal circulation

  • Placenta: The primary site of nutrient and gas exchange between the mother and the fetus
  • Umbilicar cord: contains 2 umbilical arteries and 1 umbilical vein. Umbilical vein carries oxygenated, nutrient-rich blood from placenta to fetus whereas umbilical arteries carry deoxygenated blood and waste products from fetus back to placenta.
  • Ductus venosus: duct btw umbilical vein and inferior vena cava
  • Foramen ovale: opening brw right and left atria of blood allowing blood to bypass non-functional fetal lung
  • Ductus arteriosus: duct btw pulmonary artery and aorta
• Pathway of Fetal Blood Circulation

  1. Oxygenated blood from placenta

  2. Enters umbilical vein

  3. Majority enters ductus venosus, which directs it into IVC

  4. Smaller portion flows through liver before entering IVC

  5. Blood in IVC (oxygenated blood) enters RA

  6. Most of this blood passes through foramen ovale to LA

  7. From LA to LV to aorta (oxygenated blood to upper body and brain)

  8. Deoxygenated blood from upper body returns to RA via SVC

  9. Blood in RA that doesn't pass through foramen ovale goes to RV to pulmonary artery

  10. Due to high resistance in fetal lungs, most of this blood is diverted through ductus arteriosus into the descending aorta, bypassing lungs

  11. Blood in descending aorta supplies lower body

  12. Deoxygenated blood returns to placenta through two umbilical arteries originating from iliac arteries
• Changes at Birth

  • Lungs Expand: baby takes first breath,lungs expand, pulmonary resistance drops.
  • Closure of Fetal Shunts:
  • increased pressure in LA relative to RA causes foramen ovale to close, forming fossa ovalis.
  • Ductus Arteriosus: Closes within first few days after birth due to increased oxygen levels and decreased prostaglandins, becoming ligamentum arteriosum.
  • Ductus Venosus: Closes and becomes ligamentum venosum.
  • The umbilical arteries and vein close off forming (medial umbilical ligaments and ligamentum teres hepatis).
  • Blood begins to flow into the lungs for oxygenation.
• Adult derivatives of fetal structures

  
• Fetal circulation

  
• ligamentum arteriosus

  
• Fetal circulation