Lecture on Fetal Circulation

Overview of Blood Circulation in Adults

• Blood flow in a normal adult:
  • Blood returns to the right atrium
  • Moves to the right ventricle
  • Travels to the lungs via the pulmonary arteries
  • Becomes oxygenated in the lungs
  • Returns to the left atrium via the pulmonary veins
  • Moves to the left ventricle and then to the aorta for systemic circulation

Fetal Circulation

• Oxygen Source:
  • Fetus receives oxygenated blood through the umbilical cord from the placenta, not the lungs
• Pathway:
  • Oxygenated blood comes from maternal blood supply
  • Travels down the umbilical vein to the liver
  • Moves to the heart
• Key Structures in Fetal Circulation:
  • Foramen Ovale:
    • Passageway (hole) between the left and right atrium
    • Allows oxygenated blood to pass from the right atrium to the left atrium
    • Bypasses the lungs, directing blood to systemic circulation
  • Ductus Arteriosus:
    • Connects pulmonary trunk directly to the aorta
    • Prevents unnecessary blood flow to non-functioning fetal lungs

Post-Birth Changes

• Breathing Initiation:
  • When a newborn takes its first breath:
    • Lung blood vessels dilate and resistance decreases
    • Foramen ovale closes due to reduced pressure, forming fossa ovalis (scar tissue)
  • Ductus arteriosus closes as oxygen levels rise, forming scar tissue
• Potential Abnormalities:
  • In some individuals, the foramen ovale and ductus arteriosus may remain open, causing circulatory issues

Case Study

• Will examine instances where the foramen ovale and ductus arteriosus remain open and their effects on circulation.