Lecture 11 + 12 - 2018/2017 Flashcards
How important is the placenta?
It’s very important, as it is a person’s first ever organ. In utero a baby eats via the placenta (nourished by maternal blood), and how well the placenta works determines a persons entire life (physiology).
How many women die per year caused by a pregnancy related condition?
10 women per 100,000.
How is cardiovascular mortality related to the placenta?
Women who develop pre-eclampsia are more likely to develop CVD. If you develop pre-eclampsia by 34 weeks of gestation your risk of dying from CVD has increased - even shortly after pregnancy.
What is the function of the placenta?
- Self-maintenance/renewal - the placenta needs to grow.
- Exchange/transport/transfer - maternal blood nourishes the fetus via the placenta.
- Separation - separates mum from babe (separate organisms).
- Protection from maternal infections.
- Protection from the maternal immune system.
Do maternal blood and fetal blood mix?
NO - maternal blood and fetal blood circulations are completely separate - they do not mix. However, the placenta does bring them into close apposition.
What is the placenta?
Fetal organ.
What happens around day 7 post fertilisation (day 21 of menstrual cycle) if fertilisation occurs?
The blastocyst floats around (free roaming) in the uterine cavity and on day 21 the polar trophectoderm comes into contact with the epithelial cells of the uterus and the polar trophectoderm undergoes differentiation.
What happens in differentiation when the zygote comes into contact with the uterus?
All the cells fuse and there is loss of inter-cellular boundaries - they form a cell called the primitive syncytium.
What does the primitive syncytium do in the lacunar stage (day 8-12 post fertilisation)?
It invades into the decidua and secretes enzymes which digest it. These enzymes create fluid filled gaps called lacunae.
What happens after lucanae have been formed in the decidua?
The trophectoderm is now called trophoblast protrusions - these extend into the lucane to make trabeculae.
What happens after trabeculae are formed?
The embryo sinks entirely into one wall of the uterus - the uterus heals around the embryo (embryo is completely covered).
What is the trophectoderm called once the embryo is fully implanted?
Trophoblast.
When does the lacunar stage occur?
Day 8-12 post fertilisation.
What happens after day 12 post fertilisation?
This is when the villous period beings - the primitive syncytium disappears.
What happens in the villous period?
The primitive syncytium disappears and cytotrophoblasts proliferate (push from back of embryo underneath syncytium) and become primary villi .
What happens to the lacunar system?
It has now become the intervillous space.
What happens at day 14 post fertilisation?
Cells of the extra-embryonic mesenchyme invade the primary villi to become secondary villi.
What happens at day 18-20 poster fertilisation?
Capillaries form in the secondary villi to become tertiary villi.
Where do vessels in the villi connect to?
Umbilical vessels carrying blood to and from the fetus.
What are floating villi?
These are villi that do not have contact with the maternal tissues but are suspended in the intervilllous space.
What do floating villi do?
They are responsible for the exchange and barrier functions of the placenta.
What are the chorion leave (smooth chorion) made from?
The villi that surround the side of the embryo and those that face towards the uterine lumen - they regress to form the smooth chorion.
What the chorion frondosum (definitive placenta) made from?
The viili at the base of the implantation site - they form the definitive placenta.
What are anchoring villi?
In a few villi some cytotrophoblasts break through the syncytiotrophoblast (outer layer) and spread laterally around the implantation site forming a cytotrophoblast shell.
What is the purpose of the cytotrophoblast shell?
The shell remains in contact with the maternal tissue throughout gestation.
What else do the anchoring villi do?
Columns of cyotrophoblast continue to stream out of the anchoring villi to invade the decidua (maternal endometrium) and spiral arteries - this occurs during the 1st and 2nd trimester.
What happens to the spiral arteries as the anchoring villi invade them?
The extra villous trophoblast have removed the endothelial cells and the smooth muscle cells (which make up the wall of the artery). The spiral arteries are no longer tonically active.
What happens when the spiral arteries are no longer tonically active?
This means that the spiral arteries remain open wide (don’t contract) if the mother’s SNS is activated. Normally if spiral arteries were activated by the SNS they would contract and they would keep blood from perfusing the fetus.
What happens if there is inadequate depth of trophoblast invasion in the spiral arteries?
There is still tonic control over the arteries. Therefore if the mother’s SNS is activated the spiral arteries will contract and there is a decrease in blood flow to the fetus and the placenta is malperfused. This can result in IUGR/SGA.
What happens if there is reduced number of vessels transformed?
There is far less perfusion which can result in a growth restricted baby.
What are the consequences of SGA/IUGR babies?
They are more likely to be born prematurely and or be born stillborn.
What happens to the spiral arteries at 10 weeks?
They start to plug - the arteries are plugged by endovascular trophoblasts.
What is the purpose of plugging spiral arteries?
The plug prevents the passage of maternal red blood cells to the placenta.
What is glandular milk?
It is milk which supplies nutrients to the fetus. The uterine gland empties this milk into the inter-villous space. Glandular milk is used for the first 10 weeks instead of blood from the mother.
What is premature blood flow?
This is where maternal blood flow is distributed centrally across the placenta pre -mid-gestation, whereas normal maternal blood flow is observed at the peripheries of the placenta.