Foetal circulation

Question 1

What are the 3 foetal shunts?

Answer 1

The ductus arteriosus - allows blood to bypass the lungs - connection between pulmonary arteries and the aorta - blood can go from RV-pulmonary trunk-aorta

Ductus venosus (between IVC and umbilical vein)

Foramen ovale (between the two atria - allows blood to flow from the right atrium to the left - bypassing the lungs and the right ventricle) - allows oxygenated blood to bypass the lungs

Question 2

The pulmonary vascular resistance in the foetus is high or low

Answer 2

Very high - because alveoli are closed

So flows from pulmonary arteries to the aorta

Question 3

How does the pulmonary resistance change when the baby takes first breath?

Answer 3

Decreases the vascular resistance in the pulmonary vessels

Question 4

How do the 3 foetal shunts close

Answer 4

There is a drop in the serum prostaglandins as a result of increased oxygenation of the blood from the first breath - causes closure of the ductus arteriosus.

Decrease in pulmonary vascular resistance causes a fall in pressure of the RA so LA pressure is greater which causes squashing of the atrial septum and closure of the foramen ovale.

Ductus venosus stops functioning automatically immediately after birth as umbilical cord is clamped- closes and turns into ligamentum venosus a few days later