Placenta Flashcards
What is the placenta?
Primary site of nutrient and gas exchange between mother and fetus
Cytotrophoblast
Inner layer of chorionic villi
Syncytiotrophoblast
outer layer of chorionic villi
Trophoblastic layer of cells in the blastocyst is basically what?
Placental stem cells
Implantation takes place on what day
6-7
hCG is a product of
the placenta and more specifically, trophoblast cells
What is the system responsible for the rolling of the blastocyst along the endometrium prior to implantation?
L-selectin system
Describe the L-selecting system
ok…
SO the blastocyst expresses the L-selectin
- this allows the blastocyst to weakly interact with the glycocalyx which lines the endometrial surface
and then BOOM—– hCG is secreted by the trophoblast cells of the blastocyst
What does hCG do to the endometrium
It stimulates the upregulation of TROPHININ on endometrial epithelial cells. This trophinin contain pnipodes. The blastocyst then strongly binds to the endometrial surface via the trophonin trophonin binding.
So hCG
stimulates the growth of pinopodia on the endometrium
What is decidualisation?
It is the increase in vascular permeability and secretory activity of stromal cells in the endometrium. It really is the response of the maternal cells to progesterone
What stimulates decidualisation?
Attachment….this hCG initiate process
LIF and EGF
signals that come from the endometrial stromal cells
KNOW
Decidual reaction occurs in very early pregnancy. Appears in the area where the blastocyst contacts teh endometrial decidua. Consists of an increase in secretory functions of the endometrium.
Invasion
- Within hours of attachment trophoblasts destroy epithelial cells
- Some trophoblast cells fuse and become syncytiotrophoblast
- Other trophoblast cells retain their cellularity (cytotrophoblasts)
- Finger like outgrowths called villi invade the decidua and attack blood vessels
- The villi are then invaded by embryonic blood vessels
When does this invasion occur>
first 2-3 weeks of gestation
Describe the syncytiotrophoblast
multinucleated, no cell boundaries
- invades the endometrial stroma
- Major source of hormone production, particularly hCG
So, realize that the chorionic villi is made up of the syncytiotrophoblast and the cytotrophoblast.
The chorionic villi is what invades the decidua
The arrangement of embryo surrounded by cytotrophoblast, syncytiotrophoblast, and maternal tissue remains the paradigm throughout gestation
ok
Remember, what is the most important job of the syncytiotrophoblast
secretes hCG which stimulates the corpus luteum to make progesterone during the first trimester
At what point during gestation is a vascular network established in the placenta with facilitates maternal-embryonic exchanges of gases, nutrients, and metabolic waste products
end of fourth week
secondary chorionic villi>
Early in the third week of gestation, mesenchymal tissue invades the primary chorionic villi and this forms secondary chorionic villi
Secondary chorionic villi cover….
the entire chorionic sac
chorionic villi cover the entire chorionic sac until when>
week 8 when the villi begin to be compressed. This reduces the blood supply to the villi and eventually the degenerate producing a relatively avascular area
What is this avascular area which succeedes the chorionic villi called?
smooth chorion
KNOW: Spiral arteries do not have a muscular layer which makes them very low resistance. You must have a ton of blood going to the fetus in order to make it develop, you need very low resistance vessels
In order to make make the spiral arteries good enough for this task, they must be remodeled.
What are the two mechanisms of spiral artery remodelling?
- interstitial
- intravascular
KNOW
Pre-eclampsia is caused by
faulty trophoblast invasion during pregnancy. Leads to high resistance in the spiral arteries and can cause IUGR
Pre-eclampsia is
HTN, PROTEINURIA, EDEMA
