Embryonic Membranes, Cavities and the Placenta

Question 1

Amnion

Answer 1

Membrane made by the extra-embryonic mesoderm covering the amniotic epithelium

Question 2

Chorion

Answer 2

Membrane formed by extra-embryonic mesoderm lining the trophoblast

Question 3

Rule of 2s

Answer 3

The embryo has, by the end of week two:

2 Germ Layers - Epiblast and Hypoblast
2 Trophoblast Layers - Cytotrophoblast and Syncytiotrophoblast
2 Cavities - Amniotic and Chorinioc
2 Membranes - Amnion and Chorion

Question 4

What happens to the embryo at week 4 in terms of the cavities

Answer 4

Embryo gets bigger, so the amnion must also expand

It moves across the chorion to eventually form the amnionchorion single membrane where the embryo is surrounded by amniotic fluid (filling the amniotic cavity)

Question 5

What happens to the embryo by week 6

Answer 5

Amnion continues to move towards chorion

Eventually there is contact between them

The trophoblast and extra-embryonic mesoderm become:

Smooth at abembryonic pole (away from embryo) (Chrorion Laeve)

Irregular at embryonic pole where placenta develops (Chorion Frondosum)

Question 6

Decidua - Parietalis, - Capsularis, - Basalis

Answer 6

Question 7

What happens to all the Deciduas as the embryo expands

Answer 7

The embryo obliterates the uterine cavity so the decidua capsularis eventually fuses with the decidua parietalis around/past week 8

Question 8

How does the uterus look by month 3

Answer 8

The foetus floats in the expanded amniotic cavity and the uterine cavity is gone

Decidua capsularis and parietalis have fused

Amnion and chorion form amniochorionic membrane

Question 9

Membranes in the uterus by month 3

Answer 9

Question 10

Lacunae

Answer 10

Cavities that form in syncytiotrophoblast around days 9-11 after conception as the blastocyst is further embedded in the endometrial stroma and takes over the decidua

Function as spaces to allow maternal blood to get close to foetal circulation

Question 11

What happens to the density of cytotrophoblast

Answer 11

Starts thickening and forming villi as precursors to the placenta; poking into the lacunae but still saying separate

Question 12

How does the circulation of maternal vessels work in the lacunae

Answer 12

There begins to be formation of maternal arteries and veins in the lacunae that can exchange gases and materials (not blood itself) between the maternal blood and foetal villi

Question 13

Primary, Secondary and Tertiary Villi

Answer 13

Primary (Day 13) - Small nonvascular chorionic villi containing only trophoblast

Secondary (Day 16) - Increase in size and ramify while extra-embryonic mesoderm grows into them; trophoblast and mesoderm
** Blood vessels begin developing in extra-embryonic mesoderm

Tertiary (Week 3-4) - Foetal vlood vessels develop within mesodermal core

Question 14

What does the placenta look like around weeks 3-4

Answer 14

Proper formation of foetal blood vessels into mesoderm

Cytotrophoblast breaks through syncitium and overgrows it

Stem villi become site of most exchange

Other villi anchor the vessels

Feto-Maternal Barrier consists of:
Syncytiotrophoblast
Cytotrophoblast
Mesoderm
Endothelium of foetal vessels

Question 15

Cotyledon in Human Embryo

Answer 15

Cotyledon bounded by septa begin to form by the end of week 4 in the lacunae as the stem villi branch out; all as methods to increase the absorption of nutrients

Question 16

Intravascular Barrier

Answer 16

Tissue layers between maternal and foetal blood

Question 17

Intravascular Barrier in First Trimester

Answer 17

Villi few but large, central foetal vessels to exchange surfaces are small and distances are large
Not major source of nutrition

Barrier

• A layer of syncitium
• Complete layer of cytotrophoblast
• Substantial mesoderm
• Endothelium of foetal vessels

Question 18

Intravascular Barrier in Third Trimester

Answer 18

Villi are numerous and small with peripheral foetal vessels so exchange surfaces are large and distances small

Barrier

• Syncitium Layer
• Isolated cytotrophoblast cells
• Little mesoderm
• Endothelium of foetal vessels

Question 19

Number of arteries and veins in umbilical cord

Answer 19

Two arteries, One vein

Question 20

Spiral Arteries

Answer 20

Maternal artieries that provide nutrients for the foetus in the placenta

Question 21

How much foetal blood is in the vessels within the villi and separated physically from maternal blood

Answer 21

50ml

Question 22

Placental Abruption

Answer 22

Placenta peels away from uterine wall, partially or almost completely before delivery

Deprives foetus of oxygen and nutrients - poor growth

Can cause bleeding in mother and premature birth

May cause premature or stillbirths

1 in 100 Pregnancies

Question 23

Placenta Previa

Answer 23

Low-lying placenta that covers part or all of the opening of the cervix

Can block baby’s exit from uterus

Blood vessels that connect may tear, resulting in bleeding at labour

May cause premature birth

1 in 200 pregnancies

Question 24

Placenta Accreta

Answer 24

Placenta implants too deeply and firmly into uterine wall

Placenta increta and percreta - may embed into uterine muscle or through entire uterus

May cause excessive bleeding at delivery - Well diagnosed today and managable

1 in 2500 deliveries

Question 25

Placentally-mediated conditions

Answer 25

Intra-uterine growth rertardation

Contributes to pre-eclampsia

Diabetic pregnancy

Smokers pregnancy

Pregnancy at altitude (especially when moving from low to high)

Question 26

Unusual uses of placental tissue

Answer 26

Eating the placenta cooked by mother or father (????)

Serums, Creams, Shampoo, Pills

This is just here for the ick factor you don’t need to learn it