Lecture 9 - The placenta

Question 1

why does the placenta need to separate the maternal and fetal organisms?

Answer 1

because half of the embryo will contain the paternal DNA, and the mum’s immune system would reject that

Question 2

what are the time periods of the trimesters?

Answer 2

1st trimester - conception until 12 weeks
2nd trimester - 13 weeks until 24 weeks
3rd trimester -25 weeks until term (36-40 weeks)

Question 3

At what stage in the preimplantation of the embryo do cells stop being identical?

Answer 3

Morula/advance morula - the first differential division begins creation of the inner cell mass

Question 4

what is the trophectoderm?

Answer 4

the outer blastomeres that form a hollow sphere

Question 5

from what does the inner cell mass form?

Answer 5

the inner blastomeres of the advanced morula

Question 6

The ______ ____ ____ forms the rest of the ______ and contributes a bit to the _________.

Answer 6

inner cell mass, baby, placenta

Question 7

The _________ are the sphere of cells surrounding the _____ ____ _____. This is going to become the __________ of the placenta.

Answer 7

tropectoderm, inner cell mass, trophoblast

Question 8

when does implantation happen?

Answer 8

around day 7 after fertilisation

Question 9

what orientation does the embryo implant with?

Answer 9

implants with the inner cell mass facing the uterine wall

Question 10

PICTURE A
after orientation of the embryo, the ____________ cells differentiate into _____________ and _________________. the ____________________ secrete __________ to _______ ___ _________.

Answer 10

trophoectoderm, cytotrophoblasts, syncytiotrophoblast, syncytiotrophoblast, enzymes, degrade the endometrium

Question 11

what is the primitive syncytium?

Answer 11

a syncytiotrophoblast

Question 12

PICTURE B
the ________ ____________ expands, embedding the __________ into the ___________. ______ form inside the syncytium

Answer 12

primitive syncytium, blastocyst, endometrium. Lacunae

Question 13

PICTURE C
________ fuse to form larger interconnected spaces. __________ ______ ______ are invaded and the lacunae are filled with maternal blood. embryo is almost _______, within the endometrium, with ___________ beginning to _________

Answer 13

Lacunae, maternal blood vessels, buried, epithelium, heal over it.

Question 14

PICTURE D
________ is fully ________ over, and the embryo is ______.

Answer 14

epithelium, healed, buried.

Question 15

through which period is the lacunar phase?

Answer 15

days 8-12

Question 16

what acts as nutrients for the embryo before maternal blood?

Answer 16

the primary syncytium grows into endometrial glands, which contain nutrients for the embryo

Question 17

what are trabeculae?

Answer 17

the syncitotrophoblast protrusions into the lacunae

Question 18

what do primary villi emerge from?

Answer 18

cytotrophoblasts

Question 19

what taps the maternal blood vessels?

Answer 19

lacunae

Question 20

from day 12 to the end of term, the placenta is a?

Answer 20

villous placenta

Question 21

how are primary villi formed?

Answer 21

cytotrophoblasts invading the trabeculae

Question 22

once primary villi are formed, what is the lacunar space known as?

Answer 22

intervillous space

Question 23

are there blood vessels in secondary villi?

Answer 23

no

Question 23

how are secondary villi formed and on what day?

Answer 23

at around day 14
- extraembryonic mesenchyme invade the primary villi, forming secondary villi

Question 24

how are tertiary villi formed and on what day?

Answer 24

at around day 18-20 - placental capillaries form in the villi to form tertiary villi

Question 25

what do the vessels in the villi connect to?

Answer 25

the umbilical vessels carrying blood to and from the fetus

Question 26

what statistic makes humans seem infertile as ow?

Answer 26

the fact that 60% of conceptions are lost in the first few days after conception

Question 27

what percentage of all conceptions are successful?

Answer 27

30%

Question 28

what is a villous cytotrophoblast?

Answer 28

a type of trophoblast that is found mainly in the first trimester underlying the syncytiotrophoblast

Question 29

all epithelia of the placenta come from?

Answer 29

the trophectoderm

Question 30

what is a syncytiotrophoblast?

Answer 30

the largest multinucleated cell formed from the fusion of multiple villous cytotrophoblasts

Question 31

STB does not replicated, but does what instead?

Answer 31

is replaced by fusion of additional villous cytotrophoblasts

Question 32

what cells invade and remodel the spiral arteries?

Answer 32

extravillous cytotrophoblasts EVCTB

Question 32

what is an extravillous cytotrophoblast?

Answer 32

differentiated cells that migrate from 3º villi into the decidua and myometrium

Question 33

what does the 6 week placenta look like?

Answer 33

a fluffy ball about 2-3cm in size

Question 34

true or false, the fetal side of the placenta can be seen by looking at the maternal side and flipping it over

Answer 34

false, the fetal side of the placenta is the inside

Question 35

what happens to the tertiary villi on a 7-8 week placenta?

Answer 35

they regress to form the smooth chorion

Question 36

which villi regress and which villi dont?

Answer 36

regress: villi on the sides and luminal aspect remain: villi basal to the implantation site/villi on the invading front

Question 37

what is the definitive placenta?

Answer 37

the chorion (fetal side) + the decidua basalis (maternal side) e.g the fully developed functional placenta

Question 38

what are anchoring villi?

Answer 38

The villi that break through the syncytiotrophoblast, come into contact with the uterus and stay in contact with it.

Question 39

how do the anchoring villi contribute to establishment of fetal-maternal blood flow?

Answer 39

columns of cytotrophoblasts from the anchoring villi invade the decidua and spiral arteries int he first and second trimesters

Question 40

what are floating villi?

Answer 40

villi that do not have contact with the maternal tissues but are suspended in the intervillous space

Question 41

what do floating villi do?

Answer 41

they are responsible for exchange and barrier functions of the placenta

Question 42

what type of villi make up 99% of the villi in the placenta?

Answer 42

floating villi

Question 43

after the ____________ _________ invade the spiral arteries, the arteries are transformed into ______ ____ ______ with no ________ ____ and are now lined by ___________ _____________. trophoblast columns are advancing from the ______________ ____ into the uterine stroma

Answer 43

extravillous trophoblasts, wide bore tubes, muscular wall, endovascular trophoblasts, anchoring villi

Question 44

what happens to the spiral arteries on ~day 26

Answer 44

they close

Question 45

why do spiral arteries need to be bored out?

Answer 45

to keep them open all the time, so the baby can have a constant blood flow which is independent of mums circulatory regulating mechanisms

Question 46

a shallow trophoblast invasion of the spiral arteries can cause?

Answer 46

an undergrown baby

Question 47

the decidual reactions are ________ upon implantation

Answer 47

enhanced

Question 48

what are the three layers of the decidua?

Answer 48

- decidua basalis (under implantation site) - decidua capsularis (overlying implantation site) - decidua peritalis (around the remainder of the uterus)

Question 49

The _______ cells of the decidua are swollen and store glycogen

Answer 49

stromal

Question 50

as gestation progresses, the ________ cavity enlarges, filling the _______ cavity

Answer 50

amniotic, uterine

Question 51

which two layers of the decidua fuse to the point where you can't tell them apart?

Answer 51

the decidua peritalis and the decidua capsularis

Question 52

what does the umbilical cord consist of?

Answer 52

whartons jelly, myofribroblasts and the spaces are filled with mucopolysaccharides contain 2 arteries and one vein

Question 53

what is a true knot?

Answer 53

a knot in the umbilical cord, which would theoretically close the blood vessels and prevent gas exchange

Question 54

what structure of the umbilical cord prevents true knots?

Answer 54

the whartons jelly

Question 55

if a fetus died and there was a true knot, how can we find out whether or not the knot was the cause of death?

Answer 55

by examining the whartons jelly, if it is intact, then something else killed the fetus

Question 56

true or false: the placenta has lobes

Answer 56

true