Second week of embryonic development

Question 1

what happens in the endometrial stroma on the eighth day

Answer 1

blastocyst is partially embedded in it

Question 2

what two layers does the trophoblast differentiate into

Answer 2

(1) inner layer of mononucleated cells, the cytotrophoblast,
(2) an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast

Question 3

Mitotic figures are found in the ___________ but not in the _____________

Answer 3

cytotrophoblast
syncytiotrophoblast
Thus, cells in the cytotrophoblast divide and migrate into the syncytiotrophoblast, where they fuse and lose their individual cell membranes.

Question 4

what do Cells of the inner cell mass or embryoblast also differentiate into

Answer 4

(1) a layer of small cuboidal cells adjacent to the blastocyst cavity, known as the hypoblast layer
(2) a layer of high columnar cells adjacent to the amniotic cavity, the epiblast layer

Question 5

what forms the flat disc

Answer 5

epiblast and hypoblast

Question 6

how does the amniotic cavity form

Answer 6

a small cavity appears within the epiblast which enlarges to become the amniotic cavity

Question 7

what are amnioblasts

Answer 7

Epiblast cells adjacent to the cytotrophoblast which line the amniotic cavity together with the rest of the epiblast cell

Question 8

describe the structure of the endometrial stroma adjacent to the implantation site

Answer 8

edematous and highly vascular

Question 9

what do the large, tortuous glands secrete

Answer 9

abundant glycogen and mucus

Question 10

what happens to the blastocyst on day 9

Answer 10

blastocyst is more deeply embedded in the endometrium

Question 11

what closes the penetration defect in the surface epithelium

Answer 11

a fibrin coagulum

Question 12

where does the trophoblast develop most

Answer 12

at the embryonic pole, where vacuoles appear in the syncytium

Question 13

what happens when the vacuoles in the syncytium fuse

Answer 13

they form large lacunae

Question 14

what is lacunar stage

Answer 14

fusing of vacuoles forming lacunae

Question 15

what happens at the abembryonic pole

Answer 15

flattened cells probably originating from the hypoblast form a thin membrane, the exocoelomic (Heuser’s) membrane that lines the inner surface of the cytotrophoblast

Question 16

what forms the primitive yolk sac

Answer 16

exocoelomic membrane, together with the hypoblast, forms the lining of the exocoelomic cavity, or primitive yolk sac

Question 17

On days 11 and 12 a new population of cells appears between the inner surface of the ____________ and the outer surface of the ______________

Answer 17

cytotrophoblast

exocoelomic cavity

Question 18

what are the new population of cells between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity derived from

Answer 18

derived from yolk sac cells

Question 19

what do the cells derived from yolk sac cells form

Answer 19

a fine, loose connective tissue, the extraembryonic mesoderm

Question 20

what happens to the extraembryonic mesoderm

Answer 20

fills all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally

Question 21

how does the chorionic cavity form

Answer 21

large cavities develop in the extraembryonic mesoderm, and when these become confluent, they form a new space known as the extraembryonic cavity, or chorionic cavity

Question 22

the chorionic cavity surrounds the primitive yolk sac and amniotic cavity, except

Answer 22

where the germ disc is connected to the trophoblast by the connecting stalk

Question 23

what is the

a) extraembryonic mesoderm lining the cytotrophoblast and amnion called
b) lining covering the yolk sac

Answer 23

a) extraembryonic somatic mesoderm

b) extraembryonic splanchnic mesoderm

Question 24

what does the blastocyst do in the uterus

Answer 24

produces a slight protrusion into the lumen of the uterus

Question 25

what do the lacunar spaces in the syncytium of the trophoblast form

Answer 25

an intercommunicating network still evident in the embryonic pole

Question 26

what happens as trophoblast continues to erode more and more sinusoids

Answer 26

maternal blood begins to flow through the trophoblastic system, establishing the uteroplacental circulation

Question 27

growth of the ____________ is relatively slow compared with that of the trophoblast

Answer 27

bilaminar disc which remains small

Question 28

what happens to the cells of the endometrium in the 11-12 days and what are these changes called

Answer 28

become polyhedral and loaded with glycogen and lipids; intercellular spaces are filled with extravasate, and the tissue is edematous changes–decidua reaction

Question 29

what might cause bleeding in the implantation site

Answer 29

increased blood flow into the lacunar spaces

Question 30

on day 13 what is the trophoblast characterized by

Answer 30

villous structures

Question 31

Cells of the ______________ proliferate locally and penetrate into the _________________, forming cellular
columns with the syncytial covering are known as ____________

Answer 31

cytotrophoblast
syncytiotrophoblast
primary villi

Question 32

how does the secondary yolk sac or definitive yolk sac (=Secondary umblical vesicle) form

Answer 32

hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane, they proliferate and form the secondary yolk sac within the exocoelomic cavity

Question 33

what is represented by exocolomic cysts in the chorionic cavity

Answer 33

large potions of the exocoelomic cavity that are pinched off during the formation of the secondary yolk sac

Question 34

the extraembriyonic coelom expands and forms __________

Answer 34

chorionic cavity

Question 35

what is the chorionic plate

Answer 35

extraembryonic mesoderm lining the inside of the cytotrophoblast

Question 36

what is the connecting stalk

Answer 36

only place where extraembryonic mesoderm traverses the chrionic cavity

Question 37

what happens to the connecting stalk when it develops blood vessels

Answer 37

it becomes the umbilical cord