Placenta 1 Flashcards
The placenta is a ______ organ. How is this so?
The placenta is a FETAL organ.
THe maternal blood doesn’t ever enter the fetus!
What are the 4 roles of the placenta?
- Self maintence
- Exchange/transport
- Seperation of mum from baby
- Protection from maternal infection and the maternal immune system!
How does the embryo get into the uterus?
The attached embryo that’s stuck onto the uterine wall, has enzymes in it that ‘eat into the wall’ (like jelly and a spoon). Now completely in the uterine wall ~ 4 days, very invasive.
When do tetiary villi in the placenta form?
- Around 18-20 day post conception capillaries form in the villi “tertiary villi”
- From this point on almost all villi are tertiary.
The vessels in the villi connect to the umbilical vessels carrying blood to and from the fetus.
So circulation starts in the fetus, and starts in the placenta, and then meets up
What are ‘floating/chorionic villi’?
Most villi don’t have contact with the maternal tissues, but are suspended in the intervillous space.
They ensure maximal contact with the maternal blood, and are responsible for the exchange and barrier functions of the placenta
What do the placental villi do initially?
The villi initially surround the implanted embryo.
Chorion Frondosum: what is initially formed when the villi at the base of implantation form the definitive placenta
Chorion Laeve: the villi tot he sides and towards the uterine lumen regress to form the smooth chorion
Which aspect of this is the maternal aspect in this 6 week old placenta?
They are both the maternal aspect as the placenta forms as a ball.
The embryo sits inside the ball!!
Conception happens when?….
2 weeks post the last menstrual period!
Conception ~day 14
Implantation ~day 21
The placenta forms as a sphere surrounding the embryo, but as gestation progresses what happens around week 7.5?
The villi to the sides and luminal aspect regress to form the Smooth Chorion. which is on eof the fetal membranes
Only villi basal to the implantation site remain as the definitive placenta.
Describe the anchoring villi
- Attach placenta to the uterus
- Throuhg disc continuities, in a few villi the cytotrophoblasts break through the syncytiotrophoblast to the maternal tissue
- Thy cytotrophoblast spreads laterally around the implantation site, forming a cytotrophoblast shell. WHich maintains in contact with maternal tissue throughout gestations
- Columns of cytotrophoblasr continue to stream out of these anchoring villi to invade the decidua and spiral arteries in the first and second trimesters
What happens to the uterine ‘spiral arteries’ as the placenta forms?
Extravillous trophoblasts (EVT) have broken through the syncitiotrophoblast layer of the placental villous and have invaded into the spiral arteries of the uterus.
Usually spiral arteries have muscular walls, but in pregnacy are wide-bore tubes, lined by trophoblasts.
**note the trophoblast columns anchoring the tissue to the uterus. Advancing from anchoring villi into the uterine stroma.
What are the normal physiological changes occuring mid gestation in the placenta?
Spiral Artery changes:
- Spiral arteries have been invaded by EVT (extra villous trophoblasts) and are lined by trophoblasts, having removed the SM and endothelial cells.
- Instead of being tonically active small vessels, they are now large open pipes; unable to respond to tonic control
A protective change for the babies survival!
What happens to the baby if the mother goes into ‘fight or flight’
If the uterine spiral arteries contracted → interrupted perfusion of the placenta → hypoxia ischaemic damage → reduced oxygen to the fetal brain → brain damage of the fetus
By taking control of the blood supply in the uterus, and not allowing for tonic control of the spiral arteries the fetus is not used in expense.
Maintain a controlled supply of maternal blood tot he placenta
By mid gestation, how far into the mother has the spiral arteries reached?
By mid gestation, the spiral arteries have been transformed as far as the inner 1/3 of the myometrium.
Through decidua/epithelium → inner third of myometrium
BUT inadequate development can stop tranformation to an appropriate length
What happens if there is inadequate transformation of spiral arteries like this?..
- Less depth of transformation → placenta isn’t well perfused
- Some of the arteries are still tonically controlled, and are not those open wide tubes as should be.
- Therefore the amount of blood that can pass through that vessel at a given second is less
What happens if some spiral arteries aren’t transformed at all?
That vessel is fully tonically active (and smaller!) therefore that part of the placenta is far less perfused then it should be
What are the consequences of inadequeate transformation of spiral arteries (either partial or full)?
Leads to inadequate growth! A small gestational age babies (born early) .
SGA babies: are more likely to be born prematurely and stillborn.
Why do you have ‘plugged spiral arteries’ prior to mid gestation?
Plugged by endovascular trophoblasts, which prevents the passage of maternal RBCs to the placenta.
Allows plasma through though!
SO what is the fetus eating?
What else can the spiral arteries do apart from stopping maternal RBC?
Stop pulsitile flow from mum to placenta, which would be damaging to placenta and could even result in miscarriage!
Reason for preclinical miscarriage.
Miss-miscarriage: women look like the have signs of getting a miscarriage but issue resolves itself. Impending miscarriage was a risk due to increased BP
