Placentation

Question 2

The placenta

what forms the placenta and what are its 4 functions

for first part think fetal and maternal

for second part think gases, nutrients, getting rid of waste products and synthesis of molecules

Answer 2

Formed by both fetal and maternal tissue

Functions:
- Gaseous exchange
- Transport of nutrients
- Excretion
- Hormone and protein synthesis

Question 3

decidualisation

What is decidualisation and what are the 2 changes?

for first part think endometrium and what it prepares for

for second part:

• think what progesterone does to uterine stromal cells and what it causes them to accumulate
• think about vascularisation of the endometrium

Answer 3

• Changes in the endometrium to prepare for blastocyst implantation

changes:
- progesterone causes uterine stromal cells to swell up and accumulate glycogen and lipids for them to become decidual cells

• increased vascularisation of endometrium

Question 4

decidualisation

what cells trigger further decidualisation of uterine, what does the syncytiotrophoblast do simultaneously and what is the endometrium known as after this occurs?

for first part think blast”something”

for second part think about erosion of a uterine layer

for third part think about the name of the process decidualisation

Answer 4

Blastocysts trigger further decidualisation

Syncytiotrophoblast layer erodes endometrium simultaneously.

Endometrium now know as decidua

Question 5

decidua

What are the 3 layers of the decidua and outline their positions?

for first layer, think the word “base” and for position think about “Below” something

for second layer, think the word “capsule” and for position think “surrounding” something

for third layer, think about the word “parietal” and for position think about away from something

Answer 5

Decidua basalis: decidual layer beneath the developing embryo –> forms placenta with trophoblast

Decidua capsularis: decidual layer covering embryo

Decidua parietalis: decidual lining in uterus away from embryo

Question 6

decidua

do the decidua capsularis and parietalis do ultimately?

think about fusion due to something growing to fill something else

Answer 6

Ultimately fuse together as the gestational sac grows to fill uterine cavity

Question 7

fetal membranes

What are the 3 fetal membranes?

Answer 7

• amnion
• chorion
• yolk sac and allantois

Question 8

fetal membranes

What is the amnion and 2 features of it?

for first part, think inner

for 2 features, think:

• protection of something
• secretion of something

Answer 8

Inner membrane

2 features:

• Lines amniotic sac and protects embryo/fetus from physical damage
• Secretes amniotic fluid

Question 9

fetal membranes

What happens in oligohydramnios?

Answer 9

low volume of amniotic fluid resulting in compression of fetus

Question 10

fetal membranes

What are the yolk sac & allantois for?

think nutrition

Answer 10

early source of nutrition of embryo

Question 11

fetal membranes

What is the chorion and 4 features of it?

for first part think outside

for second part think:

• trophoblast and extra embryonic mesoderm
• think chorion frondosum
• think what the embryo is suspended in until something expands
• think about what is left behind and what this is important for

Answer 11

• Outer membrane

features:

• Formed by trophoblast and extra-embryonic mesoderm
• Gives rise to Chorion frondosum (fetal part of placenta )
• Embryo suspended in chorionic cavity until amniotic sac expands and uses up this space
• Connecting stalk is left behind, which is important for umbilical cord formation

Question 12

trophoblast changes (week2)

In week 2 of placentation:
- what forms within Syncytiotrophoblast and what is it filled with, from where does this come from and why does this happen?

• what forms and surrounds the embryo?
• what forms around the chorionic cavity?

for first part, think a name for holes beginning with “L”, think blood from a type of sinusoid and think about nutrition

for second part think a type of cavity

for third part think a type of mesoderm

Answer 12

• Lacunae form within syncytiotrophoblast and fill with blood from maternal sinusoids (sinusoidal capillaries) – important as an early source of nutrition for embryo
• chorionic cavity forms and surrounds embryo
• Extra-embryonic mesoderm forms around chorionic cavity

Question 13

chorionic villi

what are primary chorionic villi?

think cytotrophoblast, what they grow into and what this growth begins

Answer 13

Cells of the cytotrophoblast that proliferate & grow into the Syncytiotrophoblast, beginning uteroplacental circulation

Question 14

chorionic vill

what are secondary chorionic villi?

think a type of mesoderm cells, where they position and what they bring in

Answer 14

Extra-embryonic mesoderm cells that Position beneath primary chorionic villi to bring in stem cells that can differentiate into placental tissue

Question 15

chorionic villi

what are tertiary chorionic villi?

think a type of mesoderm cell and what they differentiate into

Answer 15

Extra-embryonic mesoderm cells that differentiate into blood cells and smaller blood vessels

Question 16

uteroplacental circulation

From which week does circulatory system begin to develop in embryo?

Answer 16

Week 2

Question 17

uteroplacental circulation

outline what happens from week 2 of uteroplacental cirulation formation

for step 1, think:

• embryonic blood vessels in a specific layer of villi
• what they meet
• what this thing they meet is supplied by

for step 2, think what starts to form and what this allows

for step 3 think what else starts to form and what this the allows

Answer 17

1. Embryonic blood vessels in tertiary chorionic villi meet intervillous spaces supplied by maternal spiral arteries of uterine endometrium
2. Umbilical arteries start to form allowing deoxygenated blood to leave embryo
3. Umbilical vein starts to form allowing oxygenated blood to return from chorinic villi to embryo

Question 18

uteroplacental circulation

in uternoplacental circulation, what do chorionic villi at embryonic pole do to become chorion frondosum

Answer 18

• they increase in size and number

Question 19

uteroplacental circulation

What is the basal plate of placenta called and what is the chorionic plate of placenta called and what secures these 2 plates together?

Answer 19

Basal plate: maternal decidua basalis

Chorionic plate: chorionic frondosum

• anchoring villi secures these plates together

Question 20

uteroplacental circulation

In uteroplacental circulation, what happens to chorionic villi at abembryonic pole?

think compression and smoothing

Answer 20

villi become compressed and avascular chorion laeve (means “smooth”)

Question 21

placental membrane

What is the function of the placental membrane?

think gases and nutrients

Answer 21

site of gas/nutrient exchange

Question 22

placental membrane

What are the 4 components of the placental membrane

think:

• type of capillary endothelium
• a type of connective tissue
• trophoblast beginning with “c”
• trophoblast beginning with “S”

Answer 22

• Fetal capillary endothelium
• Chorionic villus connective tissue
• Cytotrophoblast
• Syncytiotrophoblast

Question 23

placental membrane

What are examples of 2 things that can cross the placental membrane?

think:
- a type of antibodies

• a category of substances

Answer 23

Maternal antibodies

Teratogenic substances (alcohol)

Question 24

structure of placenta

How much does the placenta grow to be during the second half of pregnancy

Answer 24

22cm long and 2 cm thick

Question 25

structure of placenta

What are cotyledons?

think lobules of placenta and what they are separated from and what separates them.

Answer 25

Lobules of placenta that have been separated from the decidua (in maternal side of placenta) by septa (walls)