Lecture 9 - The placenta Flashcards
why does the placenta need to separate the maternal and fetal organisms?
because half of the embryo will contain the paternal DNA, and the mum’s immune system would reject that
what are the time periods of the trimesters?
1st trimester - conception until 12 weeks
2nd trimester - 13 weeks until 24 weeks
3rd trimester -25 weeks until term (36-40 weeks)
At what stage in the preimplantation of the embryo do cells stop being identical?
Morula/advance morula - the first differential division begins creation of the inner cell mass
what is the trophectoderm?
the outer blastomeres that form a hollow sphere
from what does the inner cell mass form?
the inner blastomeres of the advanced morula
The ______ ____ ____ forms the rest of the ______ and contributes a bit to the _________.
inner cell mass, baby, placenta
The _________ are the sphere of cells surrounding the _____ ____ _____. This is going to become the __________ of the placenta.
tropectoderm, inner cell mass, trophoblast
when does implantation happen?
around day 7 after fertilisation
what orientation does the embryo implant with?
implants with the inner cell mass facing the uterine wall
PICTURE A
after orientation of the embryo, the ____________ cells differentiate into _____________ and _________________. the ____________________ secrete __________ to _______ ___ _________.
trophoectoderm, cytotrophoblasts, syncytiotrophoblast, syncytiotrophoblast, enzymes, degrade the endometrium
what is the primitive syncytium?
a syncytiotrophoblast
PICTURE B
the ________ ____________ expands, embedding the __________ into the ___________. ______ form inside the syncytium
primitive syncytium, blastocyst, endometrium. Lacunae
PICTURE C
________ fuse to form larger interconnected spaces. __________ ______ ______ invade. embryo is almost _______, with ___________ beginning to _________
Lacunae, maternal blood vessels, buried, epithelium, heal over it.
PICTURE D
________ is fully ________ over, and the embryo is ______.
epithelium, healed, buried.
through which period is the lacunar phase?
days 8-12
what acts as nutrients for the embryo before maternal blood?
the primary syncytium grows into endometrial glands, which contain nutrients for the embryo
what are trabeculae?
the cytotrophoblast protrusions into the lacunae
what do primary villi emerge from?
trabeculae
what taps the maternal blood vessels?
lacunae
from day 12 to the end of term, the placenta is a?
villous placenta
how are primary villi formed?
cytotrophoblasts invading the trabeculae
once primary villi are formed, what is the lacunar space known as?
intervillous space
are there blood vessels in secondary villi?
no
how are secondary villi formed and on what day?
at around day 14
- extraembryonic mesenchyme invade the primary villi, forming secondary villi
how are secondary villi formed and on what day?
at around day 18-20
- placental capillaries form in the villi to form tertiary villi
what do the vessels in the villi connect to?
the umbilical vessels carrying blood to and from the fetus
what statistic makes humans seem infertile as ow?
the fact that 60% of conceptions are lost in the first few days after conception
what percentage of all conceptions are successful?
30%
what is a villous cytotrophoblast?
a type of trophoblast that is found mainly in the first trimester underlying the syncytiotrophoblast
all epithelia of the placenta come from?
the trophectoderm
what is a syncytiotrophoblast?
the largest multinucleated cell formed from the fusion of multiple villous cytotrophoblasts
STB does not replicated, but does what instead?
is replaced by fusion of additional villous cytotrophoblasts
what cells invade and remodel the spiral arteries?
extravillous cytotrophoblasts EVCTB
what is an extravillous cytotrophoblast?
differentiated cells that migrate from 3º villi into the decidua and myometrium
what does the 6 week placenta look like?
a fluffy ball about 2-3cm in size
true or false, the fetal side of the placenta can be seen by looking at the maternal side and flipping it over
false, the fetal side of the placenta is the inside
what happens to the tertiary villi on a 7-8 week placenta?
they regress to form the smooth chorion
which villi regress and which villi dont?
regress: villi on the sides and luminal aspect
remain: villi basal to the implantation site/villi on the invading front
what is the definitive placenta?
the chorion (fetal side) + the decidua basalis (maternal side)
e.g the fully developed functional placenta
what are anchoring villi?
The villi that break through the syncytiotrophoblast, come into contact with the uterus and stay in contact with it.
how do the anchoring villi contribute to establishment of fetal-maternal blood flow?
columns of cytotrophoblasts from the anchoring villi invade the decidua and spiral arteries int he first and second trimesters
what are floating villi?
villi that do not have contact with the maternal tissues but are suspended in the intervillous space
what do floating villi do?
they are responsible for exchange and barrier functions of the placenta
what type of villi make up 99% of the villi in the placenta?
floating villi
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
extravillous trophoblasts, wide bore tubes, muscular wall, endovascular trophoblasts, anchoring villi
what happens to the spiral arteries on ~day 26
they close
why do spiral arteries need to be bored out?
to keep them open all the time, so the baby can have a constant blood flow which is independent of mums circulatory regulating mechanisms
a shallow trophoblast invasion of the spiral arteries can cause?
an undergrown baby
the decidual reactions are ________ upon implantation
enhanced
what are the three layers of the decidua?
- decidua basalis (under implantation site)
- decidua capsularis (overlying implantation site)
- decidua peritalis (around the remainder of the uterus)
The _______ cells of the decidua are swollen and store glycogen
stromal
as gestation progresses, the ________ cavity enlarges, filling the _______ cavity
amniotic, uterine
which two layers of the decidua fuse to the point where you can’t tell them apart?
the decidua peritalis and the decidua capsularis
what does the umbilical cord consist of?
whartons jelly, myofribroblasts and the spaces are filled with mucopolysaccharides
contain 2 arteries and one vein
what is a true knot?
a knot in the umbilical cord, which would theoretically close the blood vessels and prevent gas exchange
what structure of the umbilical cord prevents true knots?
the whartons jelly
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?
by examining the whartons jelly, if it is intact, then something else killed the fetus
true or false: the placenta has lobes
true
