Extraembryonic membranes

Question 1

Extraembyronic membranes aren’t merely membranes, they’re…?

Answer 1

Organs

Question 2

What is the main stage of each day in development?

Answer 2

1. Fertilisation
2. Cleavage
3. Compaction
4. Differentiation
5. Cavitation
6. Zona hatching
7. Implantation

Question 3

Which TFs are used for the 1st cell fate decision?

Answer 3

TE
= Cdx2

ICM
= Nanog + Gata6

Question 4

Which TFs are used for the 2nd cell fate decision

- of ICM?

Answer 4

EPI
= Nanog

Primitive endoderm
= Gata6

Question 5

Why do we have extra embryonic membranes?

Answer 5

Any animal w/ shell-less egg remains tied to water

• due to previous aquatic stages being maintained

Question 6

Amniotes

Answer 6

= Clade of tetrapods

• contains reptiles, birds + mammals
• all have amniotic eggs + internal fertilisation

Question 7

Amniotic egg

- what is it?

Answer 7

Series of fluid filled membranes

• enabled 1st land animals to lay eggs on dry land (freed reptiles of need to return to water to reproduce)

Question 8

Extra-embryonic tissue

- define

Answer 8

= embryo-derived tissue that won’t be part of embryo

Question 9

The 4 extra-embryonic membranes in all amniotes

Answer 9

Amnion
Allantois
Chorion
Yolk sac

Question 10

Additional extra embryonic membrane in vertebrates

Answer 10

Placenta

Question 11

Extraembryonic membranes

- define

Answer 11

Membranes surrounding embryo

Present in some invertebrates and all vertebrates

Ensure embryo protection from injury

Question 12

Yolk sac

Answer 12

1st element in gestational sac

Important in early embryonic blood supply

Most of it incorporated into primordial gut during 4th week of development

Question 13

Amniotic cavity formation

- cell layers involved

Answer 13

EPI layer

Endoderm later of yolk sac + gastrointestinal tract

Extraembryonic mesoderm + mesoderm

Question 14

Yolk sac

- 4 weeks

Answer 14

Connected to primitive digestive system

-> yolk sac contributes nutrients to embryo

Question 15

Endoderm

-forms..?

Answer 15

GI tract
Yolk sac
Allantois

Question 16

Yolk sac

- attachment in humans

Answer 16

attaches to outside of developing embryo + connect to umbilical cord via yolk stalk

Question 17

Yolk sac

- function

Answer 17

• provide nutrients in reptiles + birds
• forms intestine side branch in mammals
• preliminary circulatory system (delivers nutrients via primitive aorta)
• primitive erythroid cells emerge from yolk sac blood islands

Question 18

yolk sac
- structure?

• eventually absorbed by?

Answer 18

Extraembryonic endoderm
+ mesoderm

Into the gut of the embryo

Question 19

Allantois

- function

Answer 19

Reptiles + birds
= N waste reservoir

Takes part in placenta formation

Develops as side branch to bladder

Question 20

Allantois

- in human over development

Answer 20

Size of allantois decreases
-> becomes elongated sac + part of umbilical cord

Blood vessels of allantois develop into umbilical cord blood vessels

Allantois later becomes the urachus
= removes N waste from foetal bladder

Question 21

Urachal disorders

• how do they occur?
• effects?

Answer 21

Abnormalities w/ sealing of the channel during foetal development

Asymptomatic
Urachal Cysts can become infected

Question 22

Amniotic cavity (amnion)
- what is it?

Answer 22

Closed sac between embryo + amnion

Contains amniotic fluid

Question 23

Amniotic cavity

- structure

Answer 23

Lined w/ ectoderm

Covered w/ extra embryonic mesoderm

Question 24

Amniotic sac

- formation

Answer 24

Week 3-4
Folding of embryonic disc
-> draws amniotic membrane ventrally over embryo
-> enclosing of embryo in amniotic sac

Question 25

Amniotic fluid - circulated by? - removed by? - Low Mg+ levels associated with?

Answer 25

Foetal inhaling + swallowing Foetal exhalation + urination Preeclampsia + diabetes

Question 26

Amniotic fluid | - what is it?

Answer 26

Medium containing proteins, lipids, urea + electrolytes actively secreted by cells lining amniotic cavity

Question 27

Amniotic fluid | - early gestation

Answer 27

AF volume increases by getting water from mother' plasma + transporting it to foetus via foetal membranes

Question 28

Amniotic fluid | - week 8-10 gestation

Answer 28

Skin not keratinised | -> .:. bidirectional fluid diffusion between foetus + AF

Question 29

Amniotic fluid | - 28 week gestation

Answer 29

AF increases to max volume

Question 30

Amniotic fluid | - foetal nutrition

Answer 30

Not main source (15% of nutrients) BUT important for development + maturation of gut

Question 31

Amniotic fluid | - components

Answer 31

Amino acids Proteins Hormones GFs (EGF, Interleukin etc)

Question 32

Amniotic fluid stem cells (AFS)

Answer 32

Show some features of pluripotency | Able to differentiate into cells of all 3 germ layers

Question 33

Chorionic cavity | - structure

Answer 33

Lined w/ extra embryonic mesoderm | Covered in trophoblast cells forming vili

Question 34

Chorionic cavity | - what is it?

Answer 34

Transient fluid-filled space lost by expansion of amniotic sac - which finally fuses to chorionic membrane

Question 35

Differences between amnion + chorion

Answer 35

``` A = sac that cover embryo C = surrounds amnion ``` ``` A = absent in amphibians + fish C = present ``` ``` A = ectoderm + ExE mesoderm C = formed by TE + mesoderm ```

Question 36

Chorionic Villi | - what are they?

Answer 36

Act like barrier between maternal blood + foetal blood | - exchanges occur through vili walls

Question 37

Chorionic villi | - formation

Answer 37

Offshoots from surface of trophoblast

Question 38

Allantois | - formation

Answer 38

Outgrowth from hindgut which pushes its way into extra embryonic coelom

Question 39

Chorion | - function

Answer 39

Acts as extra embryonic lung (exchange of gases) Develops into placenta - important in respiration, excretion + nutrition

Question 40

Amnion | - function

Answer 40

Protects embryo from injury Amniotic fluid absorbs shock + prevents desiccation of embryo

Question 41

Placenta | - blood circulation

Answer 41

Maternal blood in intervillous space constantly in circulation Arteries + vein open into roof of cotyledon -> blood pressure drives blood to foetal end of intervillous space

Question 42

Placenta | - functions

Answer 42

``` Acts as lungs, kidneys liver GI system Endocrine system Immune system ``` Produces hormones to maintain pregnancy Protects foetus from mother's IS

Question 43

Placental lactogen | - what is it?

Answer 43

= hormone | - modifies metabolic state of mother during pregnancy to facilitate energy supply of the foetus

Question 44

Placental lactogen + Prolactin | - what does it effect?

Answer 44

Placenta development Altered glucose metabolism Breast development Maternal behaviour

Question 45

Prolactin | - what is it?

Answer 45

Hormone that activates breast milk production

Question 46

Placenta | - What can go wrong?

Answer 46

Amniotic bands - can contract around fingers + limbs - 1/1200 live births