Foetal Circulation

Question 1

Name the 3 foetal shunts

Answer 1

1. Ductus venosus
2. Foramen ovale
3. Ductus arteriosus

Question 2

What is the function of ductus arteriosus?

Answer 2

This shunt connects the pulmonary artery with the aorta and allows blood to bypass the pulmonary circulation.

Question 3

What is the function of ductus venosus?

Answer 3

This shunt connects the umbilical vein to the inferior vena cava and allows blood to bypass the liver.

Question 4

What is the function of foramen ovale?

Answer 4

This shunt connects the right atrium with the left atrium and allows blood to bypass the right ventricle and pulmonary circulation.

Question 5

Briefly draw foetal blood flow

Answer 5

Question 6

How does the foetal circulation change following birth?

Answer 6

The first breaths the baby takes expands the alveoli, decreasing the pulmonary vascular resistance. The decrease in pulmonary vascular resistance causes a fall in pressure in the right atrium. At this point the left atrial pressure is greater than the right atrial pressure, which squashes the atrial septum to cause functional closure of the foramen ovale, similar to a closed valve with nothing flowing through it. This then gets sealed shut structurally after a few weeks and becomes the fossa ovalis.

Prostaglandins are required to keep the ductus arteriosus open. Increased blood oxygenation causes a drop in circulating prostaglandins. This causes closure of the ductus arteriosus, which becomes the ligamentum arteriosum.

Immediately after birth the ductus venosus stops functioning because the umbilical cord is clamped and there is no flow in the umbilical veins. The ductus venosus structurally closes a few days later and becomes the ligamentum venosum.

Question 7

Recap the foetal circulation

Answer 7