Implantation - Endo of Pregnancy

Question 1

Review: What layer of the endometrium isn’t shed?

Answer 1

Basalis. (1/3rd bottom layer)
Contains the progenitor cells responsible for the proliferation/neovascularization of endometrium in the proliferative phase

Question 2

What are the normal endocrine “needs” for cycling of the endometrium? Which is more important for proliferative phase? Secretory phase?

Answer 2

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

Question 3

Endometrium receptivity is nice, but is it necessary for pregnancy?

Answer 3

Nope. Ectopic pregnancies happen.

Question 4

2 characteristics of the human embryo early in pregnancy?

Answer 4

Adhesive and invasive.

Question 5

What is the window of implantation in humans?

Answer 5

“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)

Question 6

Review: At what stage of embryological development does implantation occur?

Answer 6

Blastocyst.

Question 7

How can a 5 or 3 cell embryo exisit?

Answer 7

Divisions are not synchronous.

Question 8

How long after fertilization does the embryo implant?

Answer 8

6-7 days.

Question 9

What must a blastocyst do before attaching?

Answer 9

“Hatch” from the ZP.

Question 10

4 phases of implantation / placentation? How long does it take for this process to take place?

Answer 10

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)

Question 11

By a time a woman misses her period, the embryo is already completely imbedded.

Answer 11

Bummer.

Question 12

What’s the role of oxygen in invasion? (He emphasized this…)

Answer 12

Hypoxia is throught to drive invasion.

- DRIVES the trophoblast to go into maternal arteries

Question 13

Enzymes used in trophoblast invasion? (2+)

Answer 13

1) MMP-9
2) Urokinase (recall use as thrombolytic)
Others

Question 14

Why is the comparison of trophoblast invasion to cancer not good?

Answer 14

Because trophoblast invasion is highly regulated. And invasion eventually ARRESTS (if it does not… get placenta accreta, eclampsia etc.)

Question 15

What does hemochorial placentation mean?

Answer 15

Trophoblast cells replace endothelium of maternal blood vessels -> villi are in direct contact with maternal blood.

Question 16

How does the cross section of a chorionic villus look different between the 1st and 3rd trimester?

Answer 16

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)

Question 17

What are cytotrophoblasts and syncytiotrophoblasts?

Answer 17

Cytotrophoblasts are single-cell precursors to…

syncytiotrophoblasts - a big old multinucleated syncytium surrounding the villi.

Question 18

Which cells are in direct contact with maternal blood / responsible for transport to fetus?

Answer 18

Syncytiotrophoblasts.

Question 19

Other than invasion and exchange with maternal blood, what is a function of trophoblasts? Which specific cell type does this?

Answer 19

Endocrine: Produces hCG, progesterone, (and estrogen)

Mainly done by the syncytiotrophoblasts (the terminally differentiated trophoblasts)

Question 20

What is most pathology of pregnancy associated with?

Answer 20

Abnormal invasion / placentation.

Question 21

What is placenta previa? What must be done if this happens? Why?

Answer 21

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?)

Question 22

What part of the endometrium is shed and regrown every month?

Answer 22

Functionalis layer

- Top 2/3rds

Question 23

What 3 important things occur in Secretory phase?

Answer 23

1) Progesterone become critical
2) No change in enometrial thickness
3) Differentiation of epithelial and stromal cells

Question 24

What maintains the early pregnancy?

Answer 24

hCG which keeps the corpus luteum–> keeps up the secretion of progesterone

Question 25

Where does implantation usually occur (in endometrium)?

Answer 25

Mid posterior endometrial surface

- Fundus of uterus

Question 26

What is the role of ECM during implantation?

Answer 26

ECM is involved in invasion and cellular remodeling (that needs to occur when embryo invades maternal stroma/blood vessels)

Question 27

4 examples of obstetrical complications that result from poor trophoblast invasion?

Answer 27

1) Pre eclampsia, eclampsia
2) IUGRY
3) Preterm birth
4) Maternal mortality (placenta accreta)

Question 28

Which trophoblasts are the ones that invade?

Answer 28

The ones adjacent to the fetus (ICM)