Flashcards in Implantation - Endo of Pregnancy Deck (28)
Review: What layer of the endometrium isn't shed?
Basalis. (1/3rd bottom layer)
Contains the progenitor cells responsible for the proliferation/neovascularization of endometrium in the proliferative phase
What are the normal endocrine "needs" for cycling of the endometrium? Which is more important for proliferative phase? Secretory phase?
Estrogen and progesterone in SEQUENTIAL order (estrogen "primes" and then need to give progesterone)
ESTROGEN most important for endometrial build up (is the MAIN orchestrator of cellular proliferative activity)
PROGESTERONE critical for secretory phase
Endometrium receptivity is nice, but is it necessary for pregnancy?
Nope. Ectopic pregnancies happen.
2 characteristics of the human embryo early in pregnancy?
Adhesive and invasive.
What is the window of implantation in humans?
"20-24 days" (...into the cycle? I think...)
- this is a DEFINED WINDOW of time in which the embryo can adhere and successfully attach (progesterone is key for this)
Review: At what stage of embryological development does implantation occur?
How can a 5 or 3 cell embryo exisit?
Divisions are not synchronous.
How long after fertilization does the embryo implant?
What must a blastocyst do before attaching?
"Hatch" from the ZP.
4 phases of implantation / placentation? How long does it take for this process to take place?
1) Apposition - sit there
2) Adhesion - attach
3) Intrusion - trophoblast cells insinuate between cells
4) Invasion - thru basement membrane -> stroma -> blood vessels
Takes 7 days for embryo to become completely embedded! (From ovulation--> takes 2 weeks)
By a time a woman misses her period, the embryo is already completely imbedded.
What's the role of oxygen in invasion? (He emphasized this...)
Hypoxia is throught to drive invasion.
- DRIVES the trophoblast to go into maternal arteries
Enzymes used in trophoblast invasion? (2+)
2) Urokinase (recall use as thrombolytic)
Why is the comparison of trophoblast invasion to cancer not good?
Because trophoblast invasion is highly regulated. And invasion eventually ARRESTS (if it does not... get placenta accreta, eclampsia etc.)
What does hemochorial placentation mean?
Trophoblast cells replace endothelium of maternal blood vessels -> villi are in direct contact with maternal blood.
How does the cross section of a chorionic villus look different between the 1st and 3rd trimester?
In 1st trimester, there's a complete layer of cytotrophoblast cells surrounding fetal capillaries.
In 3rd trimester, fetal capillaries are in more direct contact with syncytiotrophoblasts. (there are fewer cytotrophoblasts)
What are cytotrophoblasts and syncytiotrophoblasts?
Cytotrophoblasts are single-cell precursors to...
syncytiotrophoblasts - a big old multinucleated syncytium surrounding the villi.
Which cells are in direct contact with maternal blood / responsible for transport to fetus?
Other than invasion and exchange with maternal blood, what is a function of trophoblasts? Which specific cell type does this?
Endocrine: Produces hCG, progesterone, (and estrogen)
Mainly done by the syncytiotrophoblasts (the terminally differentiated trophoblasts)
What is most pathology of pregnancy associated with?
Abnormal invasion / placentation.
What is placenta previa? What must be done if this happens? Why?
Placenta is "central" and covers the cervix.
Must do C-section when at term.
If didn't do C-section, placenta would be delivered first, resulting in anoxia during delivery.
(probably not important for this lecture?)
What part of the endometrium is shed and regrown every month?
- Top 2/3rds
What 3 important things occur in Secretory phase?
1) Progesterone become critical
2) No change in enometrial thickness
3) Differentiation of epithelial and stromal cells
What maintains the early pregnancy?
hCG which keeps the corpus luteum--> keeps up the secretion of progesterone
Where does implantation usually occur (in endometrium)?
Mid posterior endometrial surface
- Fundus of uterus
What is the role of ECM during implantation?
ECM is involved in invasion and cellular remodeling (that needs to occur when embryo invades maternal stroma/blood vessels)
4 examples of obstetrical complications that result from poor trophoblast invasion?
1) Pre eclampsia, eclampsia
3) Preterm birth
4) Maternal mortality (placenta accreta)