Pathophys of Fetus and Placenta Flashcards
What is the placenta derived from?
Trophectoderm of developing blastocyst
Describe the flow of oxygenated blood in the fetus
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
What is a failed transformation of the spinal arteries?
When the trophoblasts don’t dilate the maternal vessels enough
What are the functions of the trophoblasts?
- Hormone production (syncytiotrophoblasts mostly)
- Nutrient transport
- Prevents immune rejection via HLA-G
Describe syncytiotrophoblasts
- Polarized epithelium
- Release hormones into maternal circulation
- ->hCG, estriol, hCS, progesterone
What is the pattern of hCG secretion during pregnancy?
- 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
What produces hCG early and late?
Early: cytotrophoblasts
Late: syncytiotrophoblasts (after 6 wks gestation)
What does hCG do?
- Maintains corpus luteum
- Stimulates mom’s thyroid by binding to TSH receptors
- If we have antisera to hCG in early gestation, get pregnancy termination
How do we monitor early pregnacny?
- hCG double times
- Distinguish between intrauterine and etopic preg
- Use ultrasound
What is the primary site of steroidogenesis
Syncytiotrophoblasts
Where do steroid hormones go after being released?
Maternal circulation
What enzyme does the fetal adrenal gland lack?
3beta HSD (dont memorize name) so it cannot convert DHEA to testosterone or estrogen
It also cannot convert pregnenolone to cortisol
What enzyme does the placenta lack?
P450c17 (dont memorize name) so it cannot convert pregnenolone to DHEA
How do the fetal adrenal gland and placenta work together?
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.
What does progesterone do?
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
What produces progesterone and until when?
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
Where is estrogen derived during pregnancy?
Early preg: derived from maternal blood stream
By wk 20: derived from fetal androgens
What are the 3 types of estrogen?
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)
What are the 2 zones of the fetal adrenal gland?
Thick inner and thin outer
Describe the inner zone of the fetal adrenal gland
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
What stimulates steroidogenesis in the fetal adrenal cortex?
fetal ACTH with no neg feedback from cortisol
What are the actions of estrogens?
- Fetal control of maternal physiology
- Vasodilation of siral arteries
- Parturition
- ->placental CRH, myometrial gap jxn formation, mammary epithelial cell proliferation
Where does maternal-fetal exchange of nutrients and waste occur?
Placental villi
What supports the corpus luteum early in preg?
hCG
