changes to foetus

• Ductus venosus

  Blood from placenta goes through liver and into inferior vena cava

  About 30% bypassing liver through ductus venosus and into inferior vena cava
• Ductus arteriosus

  Most blood from right ventricle flows through ductus arteriosus to aorta

  Bypasses lungs

  Blood in pulmonary artery to go directly to aorta
• Foramen ovale 

  Right atrium can flow directly into left atrium through foramen ovale

  Go to aorta 

  Oval opening between the two chambers 
• Newborn can no longer depend on placenta for food and oxygen 

  Lungs and liver must become fully functional - blood must flow through them
• First breath triggered by : 

  • Shock of birth
  • Slap on baby’s bottom 
  • Clamping umbilical vessels allow carbon dioxide in blood to rise, stimulating respiratory centre of brain
• Lungs expand, no longer resistance 

  • Blood flow through ductus arteriosus decrease
  • Turns into fibrous tissue 
• Larger amounts of blood return to heart from lungs 

  • Pressure in left atrium increase
  • Forces flap of foramen ovale against wall of atrium 
  • Closes opening 
• Cutting umbilical cord, blood no longer flows through umbilical vessels or ductus venosus 

  • Ductus venosus gradually constricts until it is permanently closed