Embryonic membranes and cavities and the placenta

Question 1

What does the trophoblast differentiate into

Answer 1

• Cytotrophoblast

- syncytiotrophoblast

Question 2

What does the trophoblast contribute to the formation of

Answer 2

Extraembryonic mesoderm

Question 3

What is the amnion

Answer 3

The extra-embryonic mesoderm that covers the amniotic epithelium

Question 4

What is the chorion

Answer 4

The extra-embryonic mesoderm that lines the trophoblast

Question 5

What does the hypoblast produce

Answer 5

Produces cells which form the primitive (primary) yolk sac

Question 6

What forms the definitive (secondary) yolk sac and when

Answer 6

Epiblast at the time of gastrulation

Question 7

What week does the fetus float around in the amniotic fluid

Answer 7

Week 4

Question 8

What happens in week 4

Answer 8

• amniotic cavity enlarges faster than the chorionic cavity and gradually obliterates it
• eventually the amnion and chorion join and the fetus floats in the amniotic fluid

Question 9

What is the chorion made of

Answer 9

-trophoblast and extra-embryonic mesoderm

Question 10

What does the chorion become

Answer 10

• Smooth (chorion leave)

- irregular (chorion frondosum)

Question 11

Where is the smooth chorion

Answer 11

At the abembryonic pole

Question 12

Where is the irregular chorion

Answer 12

At the embryonic pole where the placenta is developing

Question 13

Where does the conceptus develop

Answer 13

In the region of the decider basalis

Question 14

What happens in week 8

Answer 14

• The expanding embryo and its coverings begin to obliterate the uterine cavity
• THe decidua capsularis eventually fuses with the decidua parietalis

Question 15

In the third month, what happens to the amnion and chorion

Answer 15

They have formed the amniochorionic cavity

Question 16

In the second week, what is the blastocyst partially embedded in

Answer 16

Endometrial stroma

Question 17

IN days 9-11, what is the blastocyst embedded in the penetration site by

Answer 17

A fibrin clot

Question 18

IN days 9-11, what happens at the embryonic pole

Answer 18

Lacunae form in the syncytiotrophoblast

Question 19

What produces more cyncytiotrophoblast

Answer 19

Cytotrophoblast mitosis

Question 20

What does the production of syncytiotrophoblast do

Answer 20

Erodes and plus and remodels maternal vessels and when the plug is removed, a functioning uteroplacental circulation is established

Question 21

What happens in day 13

Answer 21

Lacunae are filled with maternal blood

Question 22

when do fetal blood vessels form?

Answer 22

Day 13

Question 23

What develops into fetal blood vessels and how

Answer 23

Villi (of fetal origin) grow into blood-filled lacunae and these come to develop fetal blood vessels which connect to the umbilical arteries and veins

Question 24

What does the feto-maternal barrier initially consist of

Answer 24

• syncytiotrophoblast
• cytotrophoblast
• MEsoderm
• endothelium of fetal vessels

Question 25

In week 2, what is the placenta like

Answer 25

When placental villi first form, they are called primary stem villi. They have a core of cytotrophoblast covered by a layer of syncytiotrophoblast

Question 26

Whats the placenta like in week 3

Answer 26

Secondary villi have developed a core of extra-embryonic mesoderm inside the 2 trophoblast layers

-Tertiary villi will then also develop fetal blood vessels within the mesodermal one

Question 27

How are anchoring villi formed

Answer 27

-cytotrophoblast breaks through syncytium and overgrows it

Question 28

Whats happened at the end of week 4

Answer 28

• PLacental septum forms
• Cotyledon bounded by septa
• There is a branching of stem villi into intermediate and terminal villi

Question 29

What’s the intervascular barrier

Answer 29

The tissue layers between maternal and fetal bloods

Question 30

What is the placenta like in the first trimester

Answer 30

• VIlli few but large
• Central fetal vessels (so exchange surfaces are small and distances are large)

-The barrier comprises;
a layer of syncytiotrophoblast
a complete layer of cytotrophoblast
substantial mesoderm
the endothelium of fetal vessels

Question 31

What is the placenta like in the third trimester

Answer 31

• Villi are numerous and smal
• wit peripheral fetal vessels

The barrier now comprises;
the syncytiotrophoblast
isolated cytotrophoblast layer
little mesoderm
the endothelium of fetal vessels