Placenta Flashcards
What are the essential functions of the placenta?
Self maintenance/renewal Exchange/transport/transfer Separation Protection from maternal infections protection from maternal immune system
Key point about maternal and fetal circulations
DO NOT MIX
fetal blood is brought into close apposition
What is the first stage of placenta formation and what occurs?
note after this, the ‘real’ placenta
____ stage, days -
The _____ adheres and burrows into the uterine cavity (decidua).
The ____ _____ digests and invades, leaving gaps called ____
The now called ______ (not trophectoderm) invades the lacunae, these are ______.
Note endometrium forms back around when fully embedded
Lacunar stage, days 8-12
The embryo adheres and burrows into the uterine cavity (decidua).
The priitive syncytium digests and invades, leaving gaps called lacunae.
The now called trophoblast (not trophectoderm) invades the lacunae, these are trabeculae.
Note endometrium forms back around when fully embedded
Why is it important to consider preclinical pregnancy?
30% of conceptions lost prior to implantation and 30% are lost early in pregnancy (prior to fetal heart beat, 4-7 weeks)
What occurs after day 12 post conception? Stage?
villi?
The ____ period
_______ invade the trabeculae and become primary villi (two layers, syncytiotrophoblast also)
Lacunae are now _____ spaces
About day __ cells from _____ ______ migrate, and invade the primary villi to make secondary villi (three layers?)
The villous period
Cytotrophoblasts invade the trabeculae and become primary villi (two layers, syncytiotrophoblast also)
Lacunae are now intervillous spaces
About day 14 cells from extraembryonic mesoderm migrate, and invade the primary villi to make secondary villi (three layers?)
What has been reached at about day 20 post conception?
All villi are now ____ villi.
The vessels here connect to _____ vessels. Presence of fetal capillaries is sign of tertiary villous.
Layers: _______ outside, _______, then ______, then _______.
All villi are now tertiary villi.
The vessels here connect to umbilical vessels. Presence of fetal capillaries is sign of tertiary villous.
Layers: syncytiotrophoblast outside, cytotrophoblast, then villous mesenchyme, then fetal capillaries.
What are floating villi?
Villi in the intervillous spaces. Are not in contact with maternal tissue.
Act as the barrier and exchange part of the placenta
What are the two parts of the chorion?
Chorion frondosum: the villi at the base of the implanatation site, form the defintive placenta.
Chorion laeve: villi on the side, and towards the uterine lumen regress and form the smooth part.
What are anchoring villi?
Anchor the placenta to uterus.
Cytotrophoblast cells break through the syncytiotrophoblast and invade in columns, into spiral arteries and other tissue. (Extra villous trophoblast)
What do the extra villous trophoblasts do to the spiral arteries in normal pregnancy?
Why do they do this? When is this done?
Lack of this change is bad, less perfusion. May cause brain damage, small gestational age, intra-uterine growth restriction
Invade them, and remove the endothelial cells and smooth muscle walls. As far as in as inner third of myometrium
-Now endovascular trophoblasts
If a fight or flight response (vasocnostriction) the placental perfusion will not decrease, no SM. Always good perfusion.
Mid gestation, 20 weeks ish
Purpose of the trophoblast plug
Prior to mid gestation, even prior to 12 weeks, the spiral arteries have not been opened up fully yet by the EVT’s.
Endovascular trophoblasts plug the spiral arteries to prevent maternal red blood cells reaching the csurface. Plasma still passes
Also prevents pulsatile flow of maternal blood damaging the fetus. May be cause of miscarriage?
What is the fetus feeding on prior to spiral artery invasion?
Glandular milk, produced by endometrial glands, that passes into the intervillous space. (So at about 12 weeks ish)
Definitions: Villous, villous cytotrophoblast, syncytiotrophoblast; exytravillous cytotrophoblast
Villous: Branch of placenta
VCTB: Progenitor cell, seen mostly in the first trimester. underlies STB
STB: surface layer of placenta, made by fusion of VCTB.
EVT: differentiated cells that have migrated out of the villous placenta towards maternal tissue
How does the placenta’s structure change with gestational age?
First tri: Stroma of villi becomes vascularised and cellular.
2nd tri: Cytotrophoblast layer thins
3rd tri: cytotrophoblast layer sparse
Villous branching and placental size increase
What is the maternal contribution to the placenta.
Note as fetus grows, capsularis and peritalis fuse
Decidual reaction occurs, where stromal decidual cells are swollen and produce glycoen, an energy source.
Decidua basalis: Underlying implantation site. (only place spiral arteries are changed)
Decidua capsularis: Overlies the implantation site
Decidua peritalis: Overlies rest of the uterus
