Bilaminar Germ Disc Flashcards Preview

Term I: Embryology > Bilaminar Germ Disc > Flashcards

Flashcards in Bilaminar Germ Disc Deck (14):

What layers does the trophoblast differentiate to? What are some characteristics of the layers?

Cytotrophoblast is the inner layer and is characterized by active proliferation (thus cells divide here and migrate to syncytiotrophobast). The syncytiotrophoblast is the outer layer and is the one that erodes into the maternal endometrium and makes hCG. Ultimately, the trophoblast becomes the placenta.


What is hCG and what’s its purpose

Human chorionic gonadotropin is a glycoprotein that is secreted by the syncytiotrophoblast to maintain the corpus luteum so that it maintains progesterone production. It’s the molecule tested in urine for pregnancy tests.


What are some clinical correlations related to the abnormal growth of the trophoblast with little or no embryonic tissue?

High hCG levels, usually genetically ALL paternal (double Y)—fusion with oocyte without a nucleus and duplication of spermatic chromosomes in order to be diploid.


Approximately what day does the trophoblast and embryoblast differentiate?

Day 8


What are two forms of gestational trophoblastic disease? Which one is malignant?

A: Hydatiform mole (benign), choriocarcinoma (malignant). Genetic analysis of hydatidiform moles indicates that although male and female pronuclei may be genetically equivalent, they may be different functionally. This evidence is derived from the fact that while cells of moles are diploid, their entire genome is paternal. Thus, most moles arise from fertilization of an oocyte lacking a nucleus followed by duplication of the male chromosomes to restore the diploid number. These results also suggest that paternal genes regulate most of the development of the trophoblast, since in moles, this tissue differentiates even in the absence of a female pronucleus


What layers does the embryoblast differentiate into?

Embryoblast differentiates into two layers which together form the bilaminar germ disc. The hypoblast and the epiblast.


Which layer of the embryoblast is next to the amniotic cavity?



What cell shape types do we see in the epiblast and hypoblast?

Epiblast are columnar, hypoblast are cuboidal


What’s occurring around days 11-12? Hint: Think uteroplacental circulation

The blastocyst is completely embedded in the endometrium. Cells of the syncyntiotrophoblast penetrate into and erode endothelium of maternal capillaries. With continued erosion, maternal blood flows through trophoblastic system establishing the uteroplacental circulation.


What is Heuser’s membrane and how is it formed?

Flattened cells originating from the hypoblast forms the Heuser’s membrane that lines the inner surface of the cytotrophoblast. This forms the lining of the primitive yolk sac.


Discuss the production of extraembryonic mesoderm

It fills the space between the trophoblast and the primitive (or primary) yolk sac. A reticulum forms in this space and eventually large cavities are produced within the extraembryonic mesoderm. These large cavities come together to form the chorionic cavity.


What are the boundaries of the extraembryonic somatopleuric mesoderm?

the part that is adjacent to the cytotrophoblast and the amnion


What are the boundaries of the extraembryonic splanchnopleuric mesoderm?

The part that is adjacent to the yolk sac


What is the space that develops between the splanchonopleuric and somatopleuric extraembryonic mesoderm called

the chorionic cavity