Placenta Development

Question 1

When do tertiary villi appear in placental development?

Answer 1

Day 17-21

Question 2

When is foetal circulation established?

Answer 2

Day 17-21

Question 2

Which part of the placenta is derived from the foetus?

Answer 2

Chorion frondosum

Question 3

When is foetal circulation established?

Answer 3

Day 17-21

Question 4

Which part of the placenta is derived from the mother?

Answer 4

Decidua basalis

Question 5

What forms the extraembryonic mesoderm?

Answer 5

Primary source: Cells lining the primary yolk sac
Heuser’s membrane>hypoblast>embryoblast
Secondary sources (controversial): Hypoblast>Epiblast>Trophoblast (oldest answer)

Question 6

What are the two types of trophoblasts?

Answer 6

1. Syncytiotrophoblast – multinucleated, no boundaries
2. Cytotrophoblast – mononucleated, clear boundaries

Question 7

Function of trophoblast in placenta?

Answer 7

Forms the placenta and provides nutrition (“tropho-nutrition”)

Question 8

Components of extraembryonic mesoderm?

Answer 8

Somatopleuric layer – forms chorion with trophoblast

Splanchnopleuric layer – lines yolk sac

Question 9

What is the extraembryonic coelom also called?

Answer 9

Extraembryonic cavity or extra coelomic cavity

Question 10

What is the connecting stalk?

Answer 10

Structure that connects the embryo to the trophoblast, precursor to umbilical cord

Question 11

What forms the roof and lateral wall of the amniotic cavity?

Answer 11

Amniogenic layer (formed by trophoblasts)

Question 12

Derivatives of Hypoblast?

Answer 12

Forms Heuser’s membrane, contributes to extraembryonic structures, then degenerates

Question 13

Three cavities present in the embryo?

Answer 13

1. Amniotic cavity
2. Primary yolk sac cavity
3. Intraembryonic coelomic cavity

Question 14

What forms the chorion?

Answer 14

Trophoblast + somatopleuric layer of extraembryonic mesoderm

Question 15

Extraembryonic mesoderm divides into which two layers?

Answer 15

1. Splanchnopleuric layer (visceral) → Lines the yolk sac
2. Somatopleuric layer (parietal) → Forms connecting stalk and lines amniotic sac

Question 16

Function of splanchnopleuric extraembryonic mesoderm?

Answer 16

Lines the yolk sac

Question 17

Function of somatopleuric extraembryonic mesoderm?

Answer 17

Contributes to primary umbilical cord (connecting stalk)

Lines the amniotic sac

Question 18

What are the placental membranes?

Answer 18

Amnion
Chorion

Question 19

Composition of amnion?

Answer 19

Derived from amniogenic cells (from trophoblast)

Floor made of ectoderm

Lined by somatic extraembryonic mesoderm

Question 20

What does the amnion form structurally?

Answer 20

Roof and lateral wall of the amniotic cavity

Question 21

Composition of chorion?

Answer 21

Outer trophoblast cells

Somatic extraembryonic mesoderm

Question 22

Extraembryonic mesoderm is primarily derived from?

Answer 22

Primary yolk sac ✅

(Secondary sources: Hypoblast > Epiblast > Trophoblast)

Question 23

Which mesodermal layer is common to both amnion and chorion?

Answer 23

Somatic extraembryonic mesoderm