Pathophys of Fetus and Placenta

Question 1

What is the placenta derived from?

Answer 1

Trophectoderm of developing blastocyst

Question 2

Describe the flow of oxygenated blood in the fetus

Answer 2

Oxy blood comes in through umbilical vein, shunted past liver through ductus venosus–>IVC–>R atrium–>foramen ovale–>L. atrium–>L ventricle–>ascending aorta

Blood from the SVC flows downward into the right ventricle–>pul arteries–>ductus arteriosus to bypass lungs–>descending aorta–>circulation and out umbilical arteries

Question 3

What is a failed transformation of the spinal arteries?

Answer 3

When the trophoblasts don’t dilate the maternal vessels enough

Question 4

What are the functions of the trophoblasts?

Answer 4

• Hormone production (syncytiotrophoblasts mostly)
• Nutrient transport
• Prevents immune rejection via HLA-G

Question 5

Describe syncytiotrophoblasts

Answer 5

• Polarized epithelium
• Release hormones into maternal circulation
• ->hCG, estriol, hCS, progesterone

Question 6

What is the pattern of hCG secretion during pregnancy?

Answer 6

• hCG is detected in maternal serum 8 days after ovulation (1 day post implantation)
• Levels initially double every 1.4 days
• After 5th week levels double every 2.3 days
• Placental hCG secretion declines to low levels after 10 wks

Question 7

What produces hCG early and late?

Answer 7

Early: cytotrophoblasts
Late: syncytiotrophoblasts (after 6 wks gestation)

Question 8

What does hCG do?

Answer 8

• Maintains corpus luteum
• Stimulates mom’s thyroid by binding to TSH receptors
• If we have antisera to hCG in early gestation, get pregnancy termination

Question 9

How do we monitor early pregnacny?

Answer 9

• hCG double times
• Distinguish between intrauterine and etopic preg
• Use ultrasound

Question 10

What is the primary site of steroidogenesis

Answer 10

Syncytiotrophoblasts

Question 11

Where do steroid hormones go after being released?

Answer 11

Maternal circulation

Question 12

What enzyme does the fetal adrenal gland lack?

Answer 12

3beta HSD (dont memorize name) so it cannot convert DHEA to testosterone or estrogen

It also cannot convert pregnenolone to cortisol

Question 13

What enzyme does the placenta lack?

Answer 13

P450c17 (dont memorize name) so it cannot convert pregnenolone to DHEA

Question 14

How do the fetal adrenal gland and placenta work together?

Answer 14

So the placenta can’t make DHEA, but the fetus can. And the festus can’t make estrogen, but the placenta can. DHEA from the fetus will then go to the placenta where it is converted to estradiol.

Question 15

What does progesterone do?

Answer 15

Maintains hospitable uterine environment by preparing endometrium for implantation, suppressing maternal immune rejection of trophoblasts, relaxes smooth muscle to prevent uterine contraction, prevents Ca channel biosynth and gap jxn formation to promote uterine quiescence and stop contractions

Question 16

What produces progesterone and until when?

Answer 16

Corpus luteum until 10 weeks
Placenta afterward
-progressive inc in maternal blood progesterone levels during preg, eventually receptors switch and its effects are diminished at the end of pregnancy

Question 17

Where is estrogen derived during pregnancy?

Answer 17

Early preg: derived from maternal blood stream

By wk 20: derived from fetal androgens

Question 18

What are the 3 types of estrogen?

Answer 18

E1: Estrone, 1/10th as potent as estradiol; variable levels preclude clinical applications, made mostly by placenta
E2: Estradiol: equal amts arise from maternal and fetal DHEAS
E3: Estriol, 1/100th as potent as estradiol. Most of estrogen in pregnancy. Derived from fetal adrenal only =(marker for fetal aneuploidy and wellbeing)

Question 19

What are the 2 zones of the fetal adrenal gland?

Answer 19

Thick inner and thin outer

Question 20

Describe the inner zone of the fetal adrenal gland

Answer 20

Thick inner fetal zone comprises >80% of the bulk of the gland. It rapidly involutes after delivery and it produces lots of DHEAS and very little cortisol

Question 21

What stimulates steroidogenesis in the fetal adrenal cortex?

Answer 21

fetal ACTH with no neg feedback from cortisol

Question 22

What are the actions of estrogens?

Answer 22

• Fetal control of maternal physiology
• Vasodilation of siral arteries
• Parturition
• ->placental CRH, myometrial gap jxn formation, mammary epithelial cell proliferation

Question 23

Where does maternal-fetal exchange of nutrients and waste occur?

Answer 23

Placental villi

Question 24

What supports the corpus luteum early in preg?

Answer 24

hCG