YAN PLACENTA

Question 1

Describe the structure of a blastocyst.

Answer 1

inner cell mass=embryoblast
outer cell mass=trophoblast
blastocyst cavity

Question 2

What happens to the blastocyst at day 6?

Answer 2

it implants in the endometrium! the outer trophoblastic cells invade the uterine epithelium/endometrial layer!

Question 3

What happens to the blastocyst’s trophoblast by day 8?

Answer 3

it has 2 separate layers!
Outer layer = syncytiotrophoblast
inner layer = cytotrophoblast

Question 4

What are other important features of the blastocyst on day 8?

Answer 4

amniotic cavity present
amnioblasts are there
epiblast & hypoblast are there too.

Question 5

What happens to the trophoblast of the blastocyst on day 9?

Answer 5

you see the presence of trophoblastic lacunae

Question 6

How did lacunae form in the trophoblast?

Answer 6

first you have vacuoles that form & then they fuse to form lacunae

Question 7

What are other important features of the blastocyst on day 9?

Answer 7

primitive yolk sac

fibrin coagulum: closes everything off

Question 8

What happens to the trophoblast around days 11-12?

Answer 8

uteroplacental circulation is established

**trophoblast lacunae become continuous w/ the maternal sinusoids. Therefore, maternal blood can enter circulation.

Question 9

What are other features of the kid on days 11-12?

Answer 9

extraembryonic coelom
extraembryonic somatic mesoderm
extraembryonic splanchnic mesoderm

Question 10

What happens to the trophoblast of the kid around day 13?

Answer 10

its cytotrophoblastic cell layer proliferates. It penetrates into the syncytioctrophoblastic layer. these become cellular columns & then primary villi.

Question 11

What are other features of the kid @ day 13?

Answer 11

secondary yolk sac formed

connecting stalk

Question 12

Describe the structure of a primary villus.

Answer 12

syncytiotrophoblast on the outside

cytotrophoblast on the inside

Question 13

Describe the structure of a secondary villus.

Answer 13

syncytiotrophoblast on the outside
cytotrophoblast on the inside
**mesoderm core

Question 14

Describe the structure of a tertiary villus or placental villus.

Answer 14

syncytiotrophoblast on the outside
cytotrophoblast on the inside
mesoderm core
**some of the mesoderm has become blood vessels & blood cells

Question 15

What happens at the end of the 3rd week to the trophoblast?

Answer 15

maternal vessels find their way into the intervillous spaces, forms syncytium
Note: capillaries in the mesodermal core of the villi are connected to chorionic plate, then the connecting stalk, & then the intraembyronic vessels
**radial apperance b/c of the tertiary & secondary villi

Question 16

What can you see on the fetal side of a full term placenta?

Answer 16

umbilical cord
amnion
chorionic plate w/ chorionic vessels

Question 17

What is the rate of twin conceptions?

Answer 17

about 1/90

Question 18

What percentage of twins are identical or monozygotic? What percentage of twins are fraternal or dizygotic?

Answer 18

Monozygotic: 30%
Dizygotic: 70%

Question 19

What are the 2 main variations that you see with dizygotic twins?

Answer 19

whether they share the same placenta (fused)

or have completely separate placentas

Question 20

What are the different variations that you see with monozygotic twins?

Answer 20

completely separate placentas
fused common shared placenta
shared placenta & common amniotic cavity

Question 21

What are the 4 main functions of the placenta?

Answer 21

exchange of gases
exchange of nutrients & electrolytes
transmission of maternal antibodies
hormone production

Question 22

What is the advantage of having transmission of maternal antibodies to the fetus?

Answer 22

gain of passive immunity

Question 23

Where are the hormones produced in the placenta? Which hormones are produced?

Answer 23

syncytiotrophoblast

progesterones, estrogens, hCG, somatomammotropin (placental lactogen)