Placenta function and dysfunction Flashcards
What is implantation?
loss of zona pellucida - the trophoblast cells interact with endometrial lining in the uterus - now called the blastocyst - and interacts with increased vasculature and secretory glands for nutrients
Where does implantation occur?
in the superior body of the uterus
What is an ectopic pregnancy?
where implantations occurs outside of the endometrium
What is placenta praevia?
where implantation occurs at a site within the lower uterine segment close to or covering the internal os
What is placenta accreta?
invasion and implantation that is too deep
When does the placenta begin to develop?
2nd week of pregnancy
Why is the placenta so important?
Develops first before any embryological development and the placenta ensures the foetus has all its metabolic needs catered for
What happens in week2?
2 distinct cellular layers emerge from
outer cell mass
- syncytiotrophoblast
-cytotrophoblast
inner cells mass becomes the bilaminar disk
- epiblast
- hypoblast
What does the syncytiotrophoblast do?
secretes HCG to maintain the corpus luteum
What happens to the amniotic and chorionic cavities?
initially following implantation, they are separate. But as the amniotic sac grows, the chorionic cavity disappears and just becomes 1 amniotic cavity
What are chorionic villi and where do they come from?
They come from the trophoblast cells - branch from the syncytiotrophoblast to the functional endometrium
They increase the SA in contact with the maternal blood
-Core of the chorionic villi is connective tissue that foetal blood vessels develop from
How does exchange occur?
The maternal blood vessels surround the chorionic villi to allow exchange to occur
What are they 3 stages of its development?
primary - finger-like projections of the cytrotrophoblast extend into the syncytiotrophoblast and branch
secondary - mesenchyme from the embryo invades cytotrophoblast of the primary villi and extends upwards
tertiary - foetal blood vessels form from the mesenchyme that link with foetal circulation formed by the 3rd week
the placenta now has a blood supply from the mother and the fetus and effect exchange of nutrients gases and waste products can occur
What does implantation achieve?
- establishes exchange
- anchors the placenta
- establishes maternal blood flow within the placenta
What is the barrier between maternal and fetal blood flow?
single layer of trophoblast (syncytiotrophoblast)
- starts of relatively thick as full layer of cytotrophoblast and synctiotrophoblast
- as pregnancy progresses, becomes thinner as loss of cytotrophoblast cells leaving just 1 layer of trophoblast