Lecture 15: Fetal Circulation

Question 1

Describe the location of the 4 vascular bypasses

Answer 1

foramen ovale (between atria)
ductus arteriosus (between pulmonary artery and aorta) allows the ventricles to pump in sync
ductus venosus (from umbilical vein to vena cava)
placenta (where exchange occurs)

Question 2

What role does the placenta account for?

Answer 2

lungs
gastrointestinal tract
liver (waste removal)
kidney (waste removal, electrolyte balance)

Question 3

How does fetal hemoglobin account for the lower PO2 in the placenta?

Answer 3

1) higher amounts of Hb
2) higher affinity of HbF for O2 than maternal Hb
3) Bohr effect due to lower CO2 levels so greater Hb saturation

Question 4

What changes occur when the baby is born

Answer 4

1) baby takes first breath. this is very difficult due to surface tension, but high neural drive because of low O2, high CO2 and cool temperatures. When breath is taken, pulmonary resistance decreases because of alveolar expansion, and increase in PO2 and increase in pH which causes arteriolar dilation. Umbilical arteries vasoconstrict. This increases MSFP by decreasing the venous volume reserve, also increase systemic resistance. Decrease in right atrial pressure and increase in left atrial pressure causes foramen ovale to close and fuse. Ductus arteriosus closes due to increase in aortic pressure, Po2 increase causes vasoconstriction, and there is a drop in prostaglandins.

Question 5

Discuss effects of patent foramen ovale, ventricular septal defect, patent ductus arteriosus

Answer 5

atrial septal defect: allows for blood mixing between atria, lower saturation of blood, allows clots to go to systemic ciruclation, increased risk of stroke
ventricular septal defect: more common, not as deadly. increased pressure in right heart
patent ductus arteriosus: can lead to heart failure, increased pressure in pulmonary circulation