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Repro > Placenta function and dysfunction > Flashcards

Placenta function and dysfunction Flashcards

1
Q

What is implantation?

A

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

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2
Q

Where does implantation occur?

A

in the superior body of the uterus

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3
Q

What is an ectopic pregnancy?

A

where implantations occurs outside of the endometrium

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4
Q

What is placenta praevia?

A

where implantation occurs at a site within the lower uterine segment close to or covering the internal os

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5
Q

What is placenta accreta?

A

invasion and implantation that is too deep

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6
Q

When does the placenta begin to develop?

A

2nd week of pregnancy

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7
Q

Why is the placenta so important?

A

Develops first before any embryological development and the placenta ensures the foetus has all its metabolic needs catered for

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8
Q

What happens in week2?

A

2 distinct cellular layers emerge from
outer cell mass
- syncytiotrophoblast
-cytotrophoblast

inner cells mass becomes the bilaminar disk

  • epiblast
  • hypoblast
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9
Q

What does the syncytiotrophoblast do?

A

secretes HCG to maintain the corpus luteum

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10
Q

What happens to the amniotic and chorionic cavities?

A

initially following implantation, they are separate. But as the amniotic sac grows, the chorionic cavity disappears and just becomes 1 amniotic cavity

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11
Q

What are chorionic villi and where do they come from?

A

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

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12
Q

How does exchange occur?

A

The maternal blood vessels surround the chorionic villi to allow exchange to occur

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13
Q

What are they 3 stages of its development?

A

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

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14
Q

What does implantation achieve?

A
  1. establishes exchange
  2. anchors the placenta
  3. establishes maternal blood flow within the placenta
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15
Q

What is the barrier between maternal and fetal blood flow?

A

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
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16
Q

What is the decidua and the decidual reaction?

A

Decidua is the term given to the endometrial cells that have becomed specialised following the decidual reaction. They are a thick layer of modified mucous membrane which lines the uterus during pregnancy. The modification allows modulation of the degree of invasion of the conceptus once implanted

17
Q

What happens if implantation occurs in an area with no decidua?

A

There is no decidual reaction so no control on degree of invasion - nothing to stop it invading too deep
This occurs in tubal ectopic pregnancy

18
Q

What are the maternal blood vessels called and what do they do?

A

the endometrial arteries and veins - bathe the outside of the villi in maternal blood for exchange to occur

19
Q

What are the foetal vessels called and what do they do?

A

through the umbilical arteries (pleural), waste is brough to the villi and oxygen and nutrients is taken to the fetus via the umbilical vein (singular)

20
Q

What are the broad functions of the placenta?

A
  • endocrine
  • metbaolic changes
  • transport
21
Q

What hormones are produced by the placenta?

A 
Protein;
-hCG
Steroid;
-progeseteron
-oestrogen
22
Q

What is the role of hCG and where is produced?

A

produced by the syncytiotrophoblast (pregnancy specific)
supports the secretory function of the CL
only produced in the first 2 months of pregnancy

23
Q

Why is hCG a marker of pregnancy?

A

it is secreted in maternal urine

24
Q

Why does the placenta also produce progesterone and oestrogen?

A

When the placenta becomes large enough it can take over secretion from the CL (after the first trimester) - keeps the HPG axis in the pregnant state

25
Q

What metabolic changes occur in the mother and how do they occur?

A

increase appetite due to increased progesterone - allows increased fat deposition to help support the fetus and breastfeeding
hPL - creates diabetogenic state to cause insulin resistance in the mother increasing the glucose availability to the fetus

26
Q

What are the transport functions of the placenta?

A
  • gas exchange

- immunity transfer

27
Q

What molecules cross the membrane by simple diffusion?

A

water, electrolytes, urea, uric acid, gases

28
Q

What molecules cross the membrane by facilitated diffusion?

A

glucose

29
Q

What is the rate of gaseous exchange limited by?

A

flow limited NOT diffusion limited so adequate uteroplacental circulation is required

30
Q

What happens if the uteroplacental circulation is compromised in labour?

A

contractions can lead to compression of the blood vessels causing fatal distress

31
Q

What substances are transported across the placenta by AT?

A

AA, ions, vitamins - via transporters expressed by the syncytiotrophoblast

32
Q

What immunoglobulins can cross the placenta?

A

only IgG via receptor-mediated endocytosis

33
Q

Why do they need to cross the placenta?

A

so when the baby is born they have SOME defence against infection

34
Q

What are tetrogens?

A

a drug/factor that causes malformation of an embryo

35
Q

When do teratogens have their greatest effect/

A

in the first few weeks of pregnancy (especially 3-8 as this is the key time for development) - in the foetal period, there is less risk of damaging the fetus as they are just growing (except for CNS)

36
Q

What are the harmful substances that can cross the placenta?

A
  • thalomide (limb defects)
  • alcohol (CNS)
  • theraputic drugs
  • drugs of abuse (dependancy)
  • maternal smoking
37
Q

Why is maternal smoking bad for the fetus?

A

Baby can’t get enough oxygen as the CO binds to Hb and moves into the fetus which means the fetus get lets O2 causing distress

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