Fetal Circulation

Question 1

What are the shunts in the fetal circulatory system?

Answer 1

Patent ductus arteriosus, patent foramen ovale, and the ductus venosus

Question 2

Describe fetal blood flow.

Answer 2

From the placenta blood travels to the fetus via the umbilical vein. Inside the fetus is connects to the IVC via the ductus venosus, bypassing the liver. Blood enters the right atrium and shunts to the left atrium via the foramen ovale. Some blood moves from the right atrium to the right ventricle, then to the pulmonary artery. Blood from the pulmonary artery shunts across to the aorta via the ductus arteriosus. Blood from the left ventricle is pumped out through the aorta and to systemic circulation before being carried back to the placenta via the umbilical arteries.

Question 3

In what areas of fetal circulation is blood highly oxygenated?

Answer 3

Umbilical vein and ductus venosus

Question 4

In what areas of fetal circulation is blood deoxygenated?

Answer 4

Both vena cava

Question 5

In what areas of fetal circulation is blood mixed?

Answer 5

The atria and ventricles, aorta, systemic circulation (arterial side), and umbilical arteries

Question 6

What changes to fetal circulation occur at birth?

Answer 6

Vaginal squeeze pushes fluid out of the lungs
Ductus venosus closes up when blood supply from placenta is cut off, increasing systemic vascular resistance
This increase in SVR increases afterload on left ventricle and forces the foramen ovale and ductus arteriosus closed
Increase in PCO2 vasodilates pulmonary vasculature helping to close ductus arteriosus and foramen ovale