Physiology of Fetus and Placenta

Question 1

How many cell layers are between maternal and fetal blood?

Answer 1

Just 2.

Question 2

How does fetus adapt to living at a lower PO2?

Answer 2

Fetal hemoglobin, shunts most oxygenated toward toward brain.

Question 3

What’s different about fetal hemoglobin?

Answer 3

It has a higher affinity for oxygen.

Question 4

3 important aspects of fetal vasculature (he calls them shunts)?

Answer 4

Ductus venosis - brings highly oxygenated umbilical vein blood to IVC.
Foramen ovale.
Ductus arteriosis.

Question 5

Review: What does the foramen ovale do? When does it close?

Answer 5

Shunts oxygenated blood from R. atrium to L. atrium, bypassing the lungs.
Closes when L. ventrical becomes dominant.

Question 6

Review: What does the ductus arteriosis do? When does it close?

Answer 6

Shunt from pulmonary a. to descending aorta, bypassing lungs.
Closes with baby’s first breath.

Question 7

How does the trophoblast prevent immune rejection despite paternal HLA antigens? How does this work?

Answer 7

Expression of HLA-G.

HLA-G doesn’t present antigens, but prevents killing by NK cells.

Question 8

Which cells produce hormones? What do they make? (4 things)

Answer 8

Polarized epithelium (hormones go straight to maternal blood) of the syncytiotrophoblast.
Makes hCG, hCS (don't worry about it), estriol, and progesterone.

Question 9

How many days after ovulation can hCG be detected in maternal serum if pregnancy occurred?

Answer 9

Detectable in serum 8 days later.

Question 10

hCG activity?

Answer 10

Maintain corpus luteum, binds TSH receptors.

Question 11

How is monitoring hCG levels useful?

Answer 11

Abnormal levels for gestational age can indicate problem with pregnancy.

Question 12

4 molecules unique to fetus that can be measured in maternal serum?
Utility of measuring them?

Answer 12

Alpha-fetoprotein, unconjugated estriol, hCG, inhibin A.

Abnormal levels can be indicative of chromosomal abnormalities.

Question 13

What’s special about fetal adrenal steroid production?

Answer 13

The fetal adrenal glands must work with the placenta, because each has a necessary enzyme that the other lacks.
Placenta can make progesterone, but not E2 from it.
Fetal adrenal can make E2 from progesterone, but can’t make progesterone from cholesterol.

Question 14

What enzyme do the fetal adrenals lack? What does it do?

Answer 14

Lacks 3beta-HSD.
Converts DHEA to T and estrogens,
pregnenolone to cortisol.
(probably not a high yield fact)

Question 15

What enzyme for steroid production does the placenta lack?

Answer 15

Lacks P450c17 for conversion of pregnenolone to DHEA.

probably not a high yield fact

Question 16

Effect of progesterone on immune system?

Answer 16

Inhibits production of cytolytic cytokines that might cause trophoblast rejection.

Question 17

What’s the main starting material that the placenta used to make estrogens?

Answer 17

DHEA-sulfate (DHEAS) from fetal adrenals.

Question 18

Which estrogen is derived almost exclusively from fetal adrenals?

Answer 18

Estriol

thus can be used to monitor fetal health

Question 19

Which part of the fetal cortex is biggest?

Answer 19

Inner fetal zone, which makes DHEAS.

and not much cortisol

Question 20

Is giving cortisol to pregnant women harmful to the fetus? What if you need to give cortisol to the fetus?

Answer 20

Not really. Fetus has enzyme that rapidly breaks it down.
(probably only up to a point.. there are all those studies on how in-utero cortisol exposure affects later outcomes)
If giving cortisol to fetus, must give synthetic kind that won’t be broken down.

Question 21

Broad effects of estrogens produced by placenta?

Answer 21

Change maternal physiology.
Increase uterine blood supply.
Promote partuition (via CRH, myometrial gap junctions).
Promote breast maturation for lactation.