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Flashcards in Implantation and Placentation Deck (29)
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What causes the endometrium to thicken during the proliferative phase of the cycle?

estradiol alone


What are the 2 layers of the endometrium? Describe them.

-Basal 1/3 when endometrium is at its full thickness.
-Contains epithelial, stromal, vascular progenitor cells responsible for proliferation and neovascularization of the endometrium during the proliferative phase of the cycle
-Occurs under regulation of estrogen

-Top 2/3 when endometrium is at its full thickness.
-Sheds during menstruation


What is the proliferative stage and what hormone does it depend on?

First half of the cycle during which there is cellular proliferative activity. Estrogen ONLY


What is the secretory phase and what hormone is critical?

1. Progesterone critical
2. NO change in thickness
3. Differentiation of epithelial and stromal cells to allow for adhesion and invasion (ie endometrium becomes receptive)


What is endometrial receptivity?

Period of endometrial maturation, which permits the attachment of the embryo and the establishment of pregnancy. Progesterone is critical in the development of the receptive endometrium


Is the human embryo adhesive itself?

Yes, it can adhere to a fallopian tube or the peritoneal surface etc.


What is the defined period during which the embryo can successful implant on the endometrium?

Day 20-24 of cycle. Day 6-7 days post-fertilization


What maintains early pregnancy?

HCG, produced by the embryo, prevents degeneration of the corpus luteum by binding to LH receptors of the luteal cells


At what stage of embryo development does implantation occur?



How can a "5" or "3" celled embryo exist?

Divisions of early embryo cells are not synchronized


What is embryo hatching?

The ZP is dissolved by enzymes elaborated by the dev embryo


How many days does it take to get through all 4 stages of implantation?



Name the 4 stages of implantation

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


Describe apposition

Hatched blastocyst is positioned in apposition to the endometrial epithelial cells


Describe adhesion

Trophoblast cells adj to inner cell mass adhere to the apical surface of the endometrial epithelial cells


Describe intrusion

Trophoblast cells insinuate themselves IN BETWEEN the endometrial epithelial cells


Describe invasion

Trophoblast cells and then the whole embryo invade through the basement membrane and endometrial stroma and reach and invade into the maternal vessels. Commonly occurs in fundus (mid-posterior endometrial surface) of uterus


Which cells are doing the "invading"

Syncytial trophoblast cells


What is O2's role in invasion?

Trophoblast cells are sensitive to O2 levels, they seek out high O2, which is why the invade the maternal arteries. They must invade the arteries for the placenta to form.


What makes invasion different from cancer?

Invasion is highly regulated and triggered to arrest at some point.


What happens during implantation and placentation?

Invasion of maternal stroma and BVs and remodeling through secretion of ECM.


Describe the process of developing human placenta

1. Colonization of blood vessels-trophoblast cells invade maternal spiral arteries of the endometrium and replace the endothelial cells

2. Hemochorial placentation-means there is direct contact of maternal blood with trophoblast cells

3. At the core of each villus there are fetal capillaries adj to the trophoblast layer and these coalesce to form umbilical vessels
--Tree example: Soil=endometrium and maternal blood, branching roots=chorionic villi


Describe what's happening in the first trimester

Cytotrophoblasts are mitotically active and form a complete layer around the villus


Describe what's happening in the third trimester

Fetal capillaries are in closer proximity to the maternal blood because they no longer have to pass through a cytotrophoblast layer. There is inc facilitation of transport between blood and fetus


What cell promotes interaction/exchange/transport with the mother?



Describe trophoblast differentiation

Cytotrophoblasts are mitotically active progenitor trophoblast cells, which give rise the the terminally differentiated syncytiotrophoblast cells lining the outer surface of chorionic villi and come into direct contact with maternal blood


What part of blastrocyst are trophoblasts derived from?



What are the functions of the trophoblast?

Endocrine: hCG, P4, E2 secretion via syncyiotrophoblasts
-Placenta takes over hormone production from corpus luteum around week 8

Exchange: of nut and gasses


Describe some pathologies of improper placentation

Extent of trophoblast invasion may be critical and has been implicated in the development of both maternal and fetal complications later in pregnancy

Examples: pre-eclampsia/eclampsia, IUGR, preterm birth, maternal mortality