Fetal Circulation

Question 1

What does maternal blood supply the placenta with?

Answer 1

Oxygen, gas exchange, proteins, enzymes, sugars, plasma

Question 2

What makes fetal Hgb different from maternal Hgb?

Answer 2

Fetal Hgb can bind with and carry up to 20% - 30% more O2 than maternal Hgb.

Question 3

Why does placental blood have as much as 50% more O2 concentration than maternal blood?

Answer 3

Because fetal Hgb has a higher affinity to O2 than maternal Hgb. It can bind to and carry more O2 than maternal Hgb.

Question 4

What is the role of the placenta?

Answer 4

Gas exchange; delivery of all nutrients, proteins, sugars; embryonic waste removal

Question 5

What is the role of the umbilical vein?

Answer 5

To carry oxygen rich blood from the placenta to the fetus.

Question 6

How does the umbilical vein enter the fetus?

Answer 6

It passes through the umbilical ring/umbilicus and travels along the abdominal wall anteriorly.

Question 7

As the blood nears the liver, where does it go?

Answer 7

About 1/2 enters the liver, while the other 1/2 is shunted through the ductus venosus to the IVC.

Question 8

Where are fetal RBC’s produced?

Answer 8

At first they are produced in the yolk sac. At around 11-14 weeks they are produced in the liver.

Question 9

What happens when the blood reaches the IVC?

Answer 9

The O2 rich blood from the umbilical vein mixes with the low O2 blood from the lower extremities in the IVC.

Question 10

Where does blood flow from the IVC go?

Answer 10

Blood from the IVC enters the RA where most is shunted to the LA via the foramen ovale.

Question 11

Does all of the blood in the RA shunt to the LA?

Answer 11

No, some blood goes to the RV, then to the PA and on to the lungs for tissue perfusion and cell growth.

Question 12

Does all of the blood in the PA go to the lungs?

Answer 12

No, most of the blood is shunted to the AO via the ductus arteriosus.

Question 13

What is the purpose of the ductus arteriosus?

Answer 13

It helps to lower blood pressure before going to the brain.

Question 14

Where does blood from the SVC go?

Answer 14

This is returning low O2 blood from the upper extremities. It returns to the RA, where some will go to the RV and some will be shunted to the LA and on…

Question 15

Where does the blood in the descending AO go?

Answer 15

This is partially oxygenated blood and will perfuse the lower regions and lower extremities.

Question 16

Once the blood has perfused the lower regions and lower extremities, where does it go?

Answer 16

The lower O2 blood will return to the placenta for gas exchange via the 2 umbilical arteries.

Question 17

After the baby is born and the lungs inflate, what happens within the lungs?

Answer 17

Resistance in the lungs decreases.

Question 18

As a result of the post-natal decrease in resistance within the lungs, what happens within the right heart?

Answer 18

The decreased resistance within the lungs leads to an increased venous return to the right heart.

Question 19

How does the post-natal decrease in right heart pressures effect the left heart?

Answer 19

With the decrease in right heart pressures there is an increase in left heart pressures.

Question 20

When do the foramen ovale, ductus venosus, and ductus arteriosus close?

Answer 20

They should close within 48-72 hours after birth.

Question 21

What does the foramen ovale become post-natally?

Answer 21

The fossa ovalis

Question 22

What does the ductus arteriosus become post-natally?

Answer 22

The ligamentum arteriosum

Question 23

What does the ductus venosus become post-natally?

Answer 23

The ligamentum venosum

Question 24

What do the umbilical arteries become post-natally?

Answer 24

The umbilical ligament and the superior vesial artery.

Question 25

What does the umbilical vein become post-natally?

Answer 25

The ligamentum teres

Question 26

How long does it take for fetal hemoglobin to change post-natally?

Answer 26

Up to 6 months

Question 27

What is the pressure like within the fetal heart?

Answer 27

Prior to birth, pressure is higher within the right heart and lower within the left heart.