Implantation and placentation

Question 1

How is a placenta formed?

Answer 1

A placenta is formed when fetal membranes become closely attached to the uterine wall to facilitate physiological exchange of gases, nutrients and waste
products.

Question 2

What is the amnion and what does it allow?

Answer 2

Inner most fluid filled membrane in reptiles, mammals and birds.
Allows symmetrical growth and protection of fetus.
Controls temperature and allows for fetal movements.

Question 3

What does the yolk sac do?

Answer 3

Surrounds yolk in reptiles and birds.

In higher mammals has a nutritional role in early pregnancy.

Question 4

What is the allantois and what does it do?

Answer 4

It is a sac from the hindgut that goes on to form the umbilic cord when connected to the chorion.

Question 5

What is the chorion and what does it do?

Answer 5

Is the outer membrane and becomes the fetal contribution to the placenta.
All placentas are chorionic at some stage of development.

Question 6

Yolk sac membrane is also known as?

Answer 6

Viteline membrane

Question 7

What are the layers of uterine wall from outside in?

Answer 7

Perimetrium, myometrium, endometrium (glands dispersed within), uterine epithelium and uterine fluid.

Question 8

What are the three stages of implantation?

Answer 8

Apposition
— blastocyst or foetal membranes become closely
apposed to uterine lining (epithelium)
Adhesion
— a complex biochemical interaction between
molecules on the trophoblast and epithelium
. Firm attachment OR invasion of
trophoblast ¡nto uterus
— Depends on species
. Non-invasive Vs invasive

Question 9

What is the difference between an invasive or non-invasive placenta?

Answer 9

Noninvasive: Blastocyst undergoes a phase of elongation which allows the trophoblast layer to attach.

Invasive: embryo hangs around a bit before it implants. Invades into the uterine lining itself.
Uterine lining is designed to stop implantation except at appropriate times. MUC1 is downregulated to allow implantation.

Question 10

What are the fetal extraembryonic membranes?

Answer 10

Chorionic, yolk sac(midgut), and allantoic (hindgut)

Question 11

What are the two different sources of nutrition a fetus can use?

Answer 11

Hemotrophic: nutrition from circulating maternal blood.
Histotrophic: nutrition from endometrium.

Question 12

What is an epitheliochorial placenta?

Answer 12

An epitheliochorial is called this because the two membranes that touch are the outer layer epithelium of maternal origin and the chorion of fetal origin.

There are 6 layers in total.

This type is seen in the sow.

Question 13

What is an endotheliochorial placenta?

Answer 13

Endothelium on the maternal side and chorion on the fetal side.

4 layers in total.

Type seen in bitch and queen.

Question 14

What is an hemochorial placenta?

Answer 14

There are no layers on the maternal side at all.

There is only blood on the maternal side and chorion on the fetal side.

Pooling of maternal blood washes up against the fetal membrane.

Two layers of trophoblast in these species. Type found in humans and primates and mice.

Question 15

What different kinds of exchange surfaces are there in placentas?

Answer 15

Diffuse (sow and mare), Cotyledonary (Cow (convex) and Ewe (Concave)), zonary (bitch and queen) and discoid (human/primates).

Question 16

What kind of placentation does the sow have?

Answer 16

. True epitheliochorial placentation
. Diffuse
. Non-deciduate

Question 17

What does the embryotroph (uterine milk) contain in the sow?

Answer 17

• Secretions imp for development
• high P4 and E2
• Uteroferrin (purple protein):
• nutrition/Fe transport

Question 18

What kind of placenta do the ewe and cow have?

Answer 18

Synepitheliochorial
Cotyledonary
Non-deciduate

Question 19

What makes a synepitheliochorial placenta?

Answer 19

Uni-nucleate trophoblast cells undergo nuclear division without cytokinesis and you end up with Bi-Nucleate Giant cells (BNGC). These cells migrate till they reach the maternal layer where they fuse with maternal cell so you get a maternal hybrid cell and when it fuses these cell release contents into maternal circulation. Syn referes to syncitium.

Question 20

What is a placentome made of?

Answer 20

A cotyledon and caruncle together.

Cotyledon = the fetal side of the placenta. Caruncle= the maternal side of the placenta.

Question 21

What kind of placentation do horses use?

Answer 21

. Epitheliochorial placentation
. Diffuse (microcotyledons)
. But, unique to equids, there is invasive activity of
specialised trophoblast cells called “chorionic
girdle cells” which give rise to endometrial cuffs.
. Non-deciduate

Question 22

In the horse what is the chorionic girdle?

Answer 22

Two placentas exist at same time chorioviteline (yolk sac) and chorioallantois the girdle is the junction between the two placentas.

Girdle cells give rise to endometrial cups.
These cups secrete eCG (equine chorionic gonadotrophin)

Question 23

What kind of placentation do dogs use?

Answer 23

. Endotheliochorial
. Zonary (belt)
. Deciduate (looses tissue at partuition)

Question 24

What kind of placentation do humans/primates have?

Answer 24

• Haemochorial placentation
• Invasive
• Decidual
Pools of maternal blood washes up against fetal tissues, highly invasive and it is shed at parturition.

Question 25

What is decidual tissue and why is it important?

Answer 25

Decidual cells are endometrial stromal cells which proliferate and enlarge to become decidual cells
. The decidua is the maternal placenta component
. Decidual tissue is important in/to:
— communication between mother and fetus
— Limits invasion of trophoblast

Question 26

How many maternal and fetal layers are in epitheliochorial placentas?

Answer 26

3M + 3F

Question 27

How many maternal and fetal layers are in synepitheliochorial placentas?

Answer 27

3M + 3F

specialised BNGC

Question 28

How many maternal and fetal layers are in endotheliochorial placentas?

Answer 28

1M + 3F

Question 29

How many maternal and fetal layers are in haemochorial placentas?

Answer 29

0M + 3F