Implantation and Gastrulation

Question 1

Trophoblast definition

Answer 1

Primary source of the fetal component of the placenta

Question 2

Trophoblast proliferates into two cell populations:

Answer 2

Cytotrophoblast: inner layer of mitotically active mononuclear cells
Syncytiotrophoblast: a rapidly expanding, multinucleated mass in which no cell boundaries are recognizable. These were derived from cytotrophoblasts.

Question 3

Embryoblast: different germ layers:

Answer 3

Ectodermal germ layer: layer of high columnar cells. AKA Epiblast. Continuous with amnioblasts and amniotic cavity

Endodermal germ layer: layer of small cuboidal cells. AKA Hypoblast. Continuous with exocoelomic membrane and yolk sac.

Question 4

Two-layered embryoblast called:

Answer 4

Bilaminar embryonic disc

Question 5

Prechordal plate:

Answer 5

Localized area of columnar hypoblastic cells. (within endodermal germ layer)
This oropharyngeal membrane is the site of the future mouth.

Question 6

Gastrulation definition

Answer 6

Formation of the 3 germ layers. Day 14 - 19.

Question 7

Gastrulation events:

Answer 7

Bilaminar embryonic disc is converted into trilaminar embryonic disc.
Morphogenesis begins (development of body form)
First morphologic sign = formation of PRIMITIVE STREAK ***

Question 8

Description of primitive streak:

Answer 8

“a linear band of epiblast”.
Occupies half of the length of embryonic disc.
Primitive groove becomes deeper and more defined
Primitive node with pit forms at cranial end.