Implantation and Germ Layer

Question 1

What is the timeline for transport of developing embryo down the oviduct to uterus?

Answer 1

Six days. 
By the end of day one:2 cell stage 
Day 3: morula is in isthmus and corona radiata is lost
Day 4: blastocyst is in the uterus
Day 5: loss of zona pellucida
Day 6: implantation

Question 2

Blastocyst hatching?

Answer 2

Q

Question 3

Major function of ZP.

Answer 3

Surrounds developing embryo until it reaches uterus.

Question 4

What are the stages of implantation?

Answer 4

1. Attachment of expanded blastocyst to endometrial epithelium
2. Penetration of uterine epithelium
3. Invasion into tissues underlying epithelium
4. Erosion of maternal vascular supply

Question 5

Decidual reaction and importance?

Answer 5

Decidual reaction is the response of endometrial stromal cells to the invading blastocyst. Decidual cells are derived from endometrial stromatolites cells that accumulate glycogen and lipid droplets.This results in massive cellular matrix that surrounds embryo and fills most of endometrium.

Provide immunologically privileged site to protect developing embryo from being rejected.

Question 6

Ectopic pregnancies and where does it commonly occur?

Answer 6

Most commonly found in the Ampulla of the Fallopian tube, where fertilization occurs. >50%
Next most common occur in the isthmus ~25%
Third occurs in fimbriae ~17%

Question 7

When does gastrulation begin?

Answer 7

At the end of the second week of gestation.

Two-germ layer stage: consists of epiblast and hypoblast.

Question 8

What is the role of nanog and Gata6 in establishment of epiblast and hypoblast?

Answer 8

Nanog is expressed in the ICM in cells that enter early and these cells are then destined to become epiblast cells.

Gata6 is expressed when cells enter the ICM later and are destined to become hypoblast cells.
*Gata6 is induced by FGF-4

Question 9

Difference between primary and secondary yolk sac?

Answer 9

Q

Question 10

Formation of primitive streak?

Answer 10

Cell goes through cleavage to form the ICM, which then forms the Epiblast (and hypoblast). The epiblast then forms the embryonic epiblast (and amniotic ectoderm). Epiblast forms primitive streak.

Question 11

What roles might Wnt and TGF-B play in formation of primitive streak?

Answer 11

TGF-B and Wnt could possibly induce the primitive node and streak.

Question 12

What is induction?

Answer 12

Induction is

Question 13

What is the significance of primitive groove and primitive node?

Answer 13

A

Question 14

What are three classical molecular markers expressed by nodal cells?

Answer 14

A

Question 15

What are bottle cells and what role do they play in gastrulation?

Answer 15

They extend themselves. Through the layer of epiblast into the space btw epiblast and hypoblast. They become mesenchymal cells that will become part of the mesodermal germ layer.

Question 16

How does the expanded blastocyst attach to endometrial epithelium? (1st step in implantation)

Answer 16

Integrins are expressed by endometrium and trophoblast cells facilitate the attachment. The initial contact is between endometrial surface and embryonic pole of blastocyst.

Question 17

How does penetration of the Uterine Epithelium and Invasion into underlying epithelium occur?

Answer 17

Syncytiotrophoblast projections penetrate the endometrial basal laminators and invade the stream. Trophoblastic lacunae appear and eroded endometrial blood vessels fill the lacunae with maternal blood and the trophoblast is less invasive.

Question 18

What is the syncytiotrophoblast?

Answer 18

Cells lose individual identity the cell membrane fuse together. This is closest to the endometrium.

Question 19

When is the worst time during pregnancy for introduction to teratogens?

Answer 19

First four weeks

Question 20

What week of gestation do the germ layers form, and from what layer?

Answer 20

Form during third week of gestation from the epiblast.

Question 21

What happens after blastulation?

Answer 21

Gastrulation, where the embryonic germ layers form.

Question 22

What Transcription factor is related with epithelial mesenchymal cell transformation?

Answer 22

Snail