Fetal erythropoiesis and circulation

Question 1

What is the order of organs in which fetal erythropoiesis occurs?

Answer 1

Yolk Sac, Liver, Spleen, Bone

Question 2

When does fetal erythropoiesis occur in the yolk sac?

Answer 2

3-8 weeks

Question 3

When does fetal erythropoiesis occur in the liver?

Answer 3

6 weeks-birth

Question 4

When does fetal erythropoiesis occur in the spleen?

Answer 4

10-28 weeks of development.

Question 5

When does erythropoiese occur in the bone marrow?

Answer 5

18 weeks of development to adult.

Question 6

Do embryos have different hemoglobins?

Answer 6

Yes weird little funky guys. Two zeta chains, two epsilon chains.

Question 7

What is fetal hemoglobin composed of?

Answer 7

Two alphas, two gammas.

Question 8

What is adult hemoglobin composed of?

Answer 8

Two alphas, two betas.

Question 9

How does HbF manage to extract oxygen from maternal hemoglobin across the placenta?

Answer 9

It has a greater affinity for oxygen.

Question 10

What does 2-3BPG have to do with hemoglobin?

Answer 10

2,3BPG is an allosteric effector in the relationship between hemoglobin and oxygen. With adult hemoglobin, it binds better to deoxygenated hemoglobin than oxygenated hemoglobin. When it binds to a hemoglobin who has already lost some oxygen, it promotes the release of remaining oxygen molecules for delivery to the tissues.

Question 11

Where is 2-3BPG produced?

Answer 11

In the RBCs by 2-3BP Mutase. Skips an ATP-producing step in glycolysis, but favors greater oxygen delivery to tissues.

Question 12

What does 2-3BPG have to do with fetal hemoglobin?

Answer 12

Has a lower affinity for fetal hemoglobin, so it allows for HbF to extract O2 from maternal HbA across the placenta.

Question 13

What happens to HbF after birth?

Answer 13

Drops down. Replaced by HbB.

Question 14

Where is oxygen saturation highest in fetal circulation?

Answer 14

Umbilical vein coming from placenta.

Question 15

Where does blood from the umbilical vein first go through and why?

Answer 15

The ductus venosus, which connects umbilical vein to IVC and bypasses hepatic circulation.

Question 16

Once through the ductus venosus, where does fetal blood go?

Answer 16

To the right atrium.

Question 17

Where does oxygenated blood entering the right atrium go?

Answer 17

Through the foramen ovale, connecting to the left atrium, then left ventricle and out the ascending aorta to supply the brain.

Question 18

Where does deoxygenated blood from the SVC go?

Answer 18

Enters the right atrium, down to right ventricle, into main pulmonary artery, and through patent ductus arteriosis

Question 19

What is the ductus arteriosus?

Answer 19

Connects the pulmonary artery with the descending aorta, thereby bypassing the lungs (blood comes in from RV –> pulmonary artery –> ductus arteriosus –> descending aorta).

Question 20

Why does blood mostly go through the ductus arteriosus down the descending aorta instead of through the pulmonary artery?

Answer 20

There is very high pulmonary artery resistance due to low oxygen tension.

Question 21

But does ALL of the blood go through the ductus?

Answer 21

No a little goes through the pulmonary arteries and then comes back through pulmonary veins into left atrium, where it meets the oxygenated blood coming in from the foramen ovale.

Question 22

So, the blood leaving the left ventricle via the ascending aorta, how oxygenated is it?

Answer 22

Partially oxygenated.

Question 23

What is the first thing that happens when the infant is born and takes a breath?

Answer 23

Decrease in pulmonary resistance. This allows increased pulmonary artery flow and decreased flow across the ductus arteriosus.

Question 24

Why does left atrial pressure increase after birth?

Answer 24

With increased pulmonary artery flow, there is increased pulmonary vein flow –> increased blood flow into the left atrium

Question 25

What does increased left atrial pressure after birth cause?

Answer 25

1) Opposes flow of blood across foramen ovale (now called fossa ovalis), forces more blood through RV –> lungs.
2) Fossa ovalis closes (usually)

Question 26

What causes the closure of the ductus arteriosus?

Answer 26

Increase in O2 from respiration, and decrease in prostaglandins due to separation of placenta. Usually closed by day 4.

Question 27

What can help keep PDA open?

Answer 27

Prostaglandins E1 and E2.

Question 28

What closes the PDA when given?

Answer 28

Indomethacin (which inhibits prostaglandin synthesis).

Question 29

What is the urachus?

Answer 29

Part of the allantoic duct between bladder and umbilicus.

Question 30

What is the urachus called after birth?

Answer 30

mediaN umbilical ligament

Question 31

What does the ductus arteriosus become after birth?

Answer 31

Ligamentum arteriosum

Question 32

What does the ductus venosus become after birth?

Answer 32

ligamentum venosum.

Question 33

What does the foramen ovale become after birth?

Answer 33

Fossa ovalis/atrial septum.

Question 34

What does the notochord become after birth?

Answer 34

Nucleus pulposus.

Question 35

What do the umbiLical arteries become after birth?

Answer 35

MediaL umbilical ligaments

Question 36

What does the umbilical vein become after birth?

Answer 36

Ligamentum teres hepatis. Contained in falciform ligament.

Question 37

How does the right ventricle change after birth?

Answer 37

Becomes more compliant to accomodate increased blood flow.