Lecture 19: Implantation Flashcards
What are the two layers of the endometrium?
- Basalis layer
2. Frictionalis layer
What are the characteristics of the basalis layer?
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
What are the characteristic of the frictionalis layer?
Top 2/3 of full thickness endometrium
Shed during menses
What are the minimal endocrine “needs” for normal cycling of the endometrium?
Estrogen
Progesterone
What is the definition of endometrial receptivity?
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
Do you need endometrium to implant?
No, because in ectopic pregnancy, embryo implants in fallopian tube
What maintains the early pregnancy?
Corpus luteum, hCG maintains corpus luteum
What is the window of implantation in the human?
Days 20-24 (4 days after fertilization)
At what stage of embryo devo does implantation occur?
Blastocyst
What is significant about the blastocyst stage?
The stage at which the embryo implants
How can a “5” cell or a “3” cell embryo exist?
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)
What is embryo hatching?
When the zona pellucida is dissolved by enzymes elaborated by the developing embryo
What are the phases of human implantation and placentation?
- Apposition
- Adhesion
- Intrusion
- Invasion
What is apposition?
First stage of implantation
When the hatched blastocyst is positioned in apposition to the endometrial epithelial cells
What is adhesion?
2nd stage of implantation
The trophoblast cell adjacent to the inner cell mass (ICM) adhere to the apical surface of the endometrial epithelial cells
What is intrusion?
3rd stage of implantation
The trophoblast cells insinuate themselves in between the endometrial epithelial cells
What is invasion?
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
How long does it take to implant?
7 days (12-14 days post ovulation)
How long does it take from fertilization to implantation?
2 weeks
How does embryo get to uterus?
Rolls from tube to uterus
Mucins slow it down
What role does oxygen play in implantation?
Oxygen gradient is what drives trophoblast to invade maternal vessels
That’s why trophoblast doesn’t invade veins because less oxygen
What is CAM?
Cell adhesion molecules (CAMs)
Where does implantation usually take place?
Implantation occurs at mid posterior endometrial surface
What enzymes are involved in implantation?
- MMP-9
2. Urokinase type plasminogen activator
Why is cancer cell invasion a poor analogy for torphoblast implantation?
Because trophoblast invasion is a REGULATED process with specific factors hypothesized to be involved (factors still under research)
Cancer growth is UNregulated
What does syncytiotrophoblast eventually do to endothelial cells?
Trophoblast cells replace the endothelial cells in blood vessels
When trophoblast invades, what happens?
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
What are cytotrophoblasts?
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
Where is trophoblast derived from?
Trophoblast derived from trophoectoderm of blastocyst
What is the function of trophoblast?
- . Endocrine
- secretes hCG and P4 (and E)
- Exchange: nutrients and gases are exchanged between mother and fetus
What is pre-eclampsia?
High blood pressure
Proteinuria
Precursor to eclampsia
What is eclampsia?
An acute life-threatening complication of pregnancy
TONIC-CLONIC SEIZURES
What is the clinical relevance of implantation?
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
What is placenta previa?
Placenta blocking the cervix and the outlet
