Lecture 19: Implantation

Question 1

What are the two layers of the endometrium?

Answer 1

1. Basalis layer

2. Frictionalis layer

Question 2

What are the characteristics of the basalis layer?

Answer 2

Basal 1/3 of full thickness endometrium 
NOT shed during menses
Contains:
	-epithelial
	-stromal
	-vascular PROGENITOR cells
Purpose: responsible for proliferation and neovasculartion of the endometrium during the proliferative phase

Question 3

What are the characteristic of the frictionalis layer?

Answer 3

Top 2/3 of full thickness endometrium

Shed during menses

Question 4

What are the minimal endocrine “needs” for normal cycling of the endometrium?

Answer 4

Estrogen

Progesterone

Question 5

What is the definition of endometrial receptivity?

Answer 5

Period of endometrial maturation, which permits the attachment of the embryo and the establishment of pregnancy
PROGESTERONE is critical in devo of receptive endometrium
Human embryo is very “adhesive” and “invasive”
-there is a DEFINED period that the embryo can adhere and implant in endometrium

Question 6

Do you need endometrium to implant?

Answer 6

No, because in ectopic pregnancy, embryo implants in fallopian tube

Question 7

What maintains the early pregnancy?

Answer 7

Corpus luteum, hCG maintains corpus luteum

Question 8

What is the window of implantation in the human?

Answer 8

Days 20-24 (4 days after fertilization)

Question 9

At what stage of embryo devo does implantation occur?

Answer 9

Blastocyst

Question 10

What is significant about the blastocyst stage?

Answer 10

The stage at which the embryo implants

Question 11

How can a “5” cell or a “3” cell embryo exist?

Answer 11

If there is a lag between mitoses between two cells (as in two cells goes to 4…but then only one cell divides while the other three is senescent…this leads to 5 cells)

Question 12

What is embryo hatching?

Answer 12

When the zona pellucida is dissolved by enzymes elaborated by the developing embryo

Question 13

What are the phases of human implantation and placentation?

Answer 13

1. Apposition
2. Adhesion
3. Intrusion
4. Invasion

Question 14

What is apposition?

Answer 14

First stage of implantation

When the hatched blastocyst is positioned in apposition to the endometrial epithelial cells

Question 15

What is adhesion?

Answer 15

2nd stage of implantation
The trophoblast cell adjacent to the inner cell mass (ICM) adhere to the apical surface of the endometrial epithelial cells

Question 16

What is intrusion?

Answer 16

3rd stage of implantation

The trophoblast cells insinuate themselves in between the endometrial epithelial cells

Question 17

What is invasion?

Answer 17

4th stage of implantation
The trophoblast cells and, ultimately, the whole embryo invade through the basement membrane and the endometrial stroma and reach and invade into the maternal vessels
VEGF is released to promote vasculature growth

Question 18

How long does it take to implant?

Answer 18

7 days (12-14 days post ovulation)

Question 19

How long does it take from fertilization to implantation?

Answer 19

2 weeks

Question 20

How does embryo get to uterus?

Answer 20

Rolls from tube to uterus

Mucins slow it down

Question 21

What role does oxygen play in implantation?

Answer 21

Oxygen gradient is what drives trophoblast to invade maternal vessels
That’s why trophoblast doesn’t invade veins because less oxygen

Question 22

What is CAM?

Answer 22

Cell adhesion molecules (CAMs)

Question 23

Where does implantation usually take place?

Answer 23

Implantation occurs at mid posterior endometrial surface

Question 24

What enzymes are involved in implantation?

Answer 24

1. MMP-9

2. Urokinase type plasminogen activator

Question 25

Why is cancer cell invasion a poor analogy for torphoblast implantation?

Answer 25

Because trophoblast invasion is a REGULATED process with specific factors hypothesized to be involved (factors still under research)
Cancer growth is UNregulated

Question 26

What does syncytiotrophoblast eventually do to endothelial cells?

Answer 26

Trophoblast cells replace the endothelial cells in blood vessels

Question 27

When trophoblast invades, what happens?

Answer 27

Trophoblast cells “colonize” the maternal spiral arteries of the endometrium and replace endothelial cels
There exists hemochorial placentation (when there is direct contact of maternal blood with trophoblast cells)
Image of a tree when chorionic villi of the placenta as the branching roots of tree embedded in endometrium and “bathed” in maternal blood

Question 28

What are cytotrophoblasts?

Answer 28

Mitotically active progenitor trophoblast cells
Give rise to terminally differentiated syncytiotrophoblast cells lining the outer surface of chorionic villi
-come in direct contact with maternal blood
Will be lost as you get to third trimester to let fetal capillaries to contact syncytio trophoblast directly

Question 29

Where is trophoblast derived from?

Answer 29

Trophoblast derived from trophoectoderm of blastocyst

Question 30

What is the function of trophoblast?

Answer 30

1. . Endocrine
   
   • secretes hCG and P4 (and E)
2. Exchange: nutrients and gases are exchanged between mother and fetus

Question 31

What is pre-eclampsia?

Answer 31

High blood pressure
Proteinuria
Precursor to eclampsia

Question 32

What is eclampsia?

Answer 32

An acute life-threatening complication of pregnancy

TONIC-CLONIC SEIZURES

Question 33

What is the clinical relevance of implantation?

Answer 33

Extent of trophoblast invasion may be critical and has been implicated in the development of both maternal and fetal complications later in pregnancy
Exampes: i. pre-eclampsia and eclampsia
ii. Intrauterine growth restriction (IUGR)
iii. Preterm birth
iv. Maternal mortality

Question 34

What is placenta previa?

Answer 34

Placenta blocking the cervix and the outlet