Implantation and Placentation

Question 1

What causes the endometrium to thicken during the proliferative phase of the cycle?

Answer 1

estradiol alone

Question 2

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

Answer 2

Basalis

• 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

Functionalis

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

Question 3

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

Answer 3

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

Question 4

What is the secretory phase and what hormone is critical?

Answer 4

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)

Question 5

What is endometrial receptivity?

Answer 5

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

Question 6

Is the human embryo adhesive itself?

Answer 6

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

Question 7

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

Answer 7

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

Question 8

What maintains early pregnancy?

Answer 8

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

Question 9

At what stage of embryo development does implantation occur?

Answer 9

Blastocyst

Question 10

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

Answer 10

Divisions of early embryo cells are not synchronized

Question 11

What is embryo hatching?

Answer 11

The ZP is dissolved by enzymes elaborated by the dev embryo

Question 12

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

Answer 12

7

Question 13

Name the 4 stages of implantation

Answer 13

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

Question 14

Describe apposition

Answer 14

Hatched blastocyst is positioned in apposition to the endometrial epithelial cells

Question 15

Describe adhesion

Answer 15

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

Question 16

Describe intrusion

Answer 16

Trophoblast cells insinuate themselves IN BETWEEN the endometrial epithelial cells

Question 17

Describe invasion

Answer 17

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

Question 18

Which cells are doing the “invading”

Answer 18

Syncytial trophoblast cells

Question 19

What is O2’s role in invasion?

Answer 19

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.

Question 20

What makes invasion different from cancer?

Answer 20

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

Question 21

What happens during implantation and placentation?

Answer 21

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

Question 22

Describe the process of developing human placenta

Answer 22

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

Question 23

Describe what’s happening in the first trimester

Answer 23

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

Question 24

Describe what’s happening in the third trimester

Answer 24

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

Question 25

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

Answer 25

Syncytiotrophoblasts

Question 26

Describe trophoblast differentiation

Answer 26

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

Question 27

What part of blastrocyst are trophoblasts derived from?

Answer 27

Trophectoderm

Question 28

What are the functions of the trophoblast?

Answer 28

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

Exchange: of nut and gasses

Question 29

Describe some pathologies of improper placentation

Answer 29

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