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17 Cards in this Set
- Front
- Back
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What are the two main roles of the placenta? |
1) the physical attachment of the embryo to the uterus
2) bringing of the fetal/maternal circulations into proximity allowing exchange of gases, nutrients and waste |
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Name and describe the foetal portion of the placenta. |
Chorionic plate - covered with the a vascular glossy amnion
contains the chorionic vessels (seen on the surface) |
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Name and describe the maternal portion of the placenta. |
Basal plate - made up of two tissues: > embryonic tissue (cytotrophoblast, syncytiotrophoblast) > maternal tissue (decidua basalis) |
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Identify 1-4 |
1) Cotyledon (lobe) 2) Cut edge of the amnion 3) Umbilical cord 4) Decidua |
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Describe the process of blastocyst implantation. |
Day 7 (anytime between day 7-12): trophoblast cells adjacent to the embryoblast pole start to penetrate the endometrium
Day 8: trophoblast differentiates into syncytiotrophoblast and villous cytotrophoblast. A series of fluid filled spaces known as lacunae begin to develop within the STB mass
Day 11/12: blastocyst is completely embedded in the endometrium |
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Describe how the uteroplacental circulation is formed. |
Day 11/12: STB cells erode the endothelial lining of maternal capillaries (sinusoids)
The syncytial lacunae fill with maternal blood initially but they quicly become blocked with trophoblast plugs → prevents maternal blood from entering the lacunae or intervillous space for the first 10 weeks of pregnancy |
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What is the significance of preventing the maternal blood from entering the lacunae? |
No blood flow ∴ low oxygen concentration in the intervillous space ∴ placenta and fetus experience no oxidative stress
As the trophoblast plugs dissolve oxygen conc. and oxidative stress increases - placenta produces protective anti-oxidant enzymes |
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Describe what happens in decidualisation. |
Day 11/12: cells of the endometrium grow and accumulate glycogen and lipids |
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Describe how the villous tree is formed. |
Trophoblasts that had begun to penetrate the lacunae become increasingly branched forming the chorionic villi
Beginning of wk 3 - 1° villi → 2° villi → 3° villi - end of wk 3 |
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Describe how the trophoblast adapts the maternal circulation. |
Extravillous trophoblasts invade into the maternal spiral arteries and remodels them from being high resistance (low flow) to low resistance (high flow) vessels
This allows increase of blood flow to the fetus |
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Describe the major maternal and foetal blood vessels that supply the placenta. |
Maternal: uterine arteries/veins |
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What is placental insufficiency? |
When the placenta is unable to deliver an adequate supply of nutrients and oxygen to the fetus e.g. Intrauterine growth restriction (IUGR), Pre-eclampsia |
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Describe the barker hypothesis. |
Size at birth is related to the risk of developing disease in later life reduced birthweight → increased risk of CAD, diabetes, HTN and stroke in adulthood |
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Define pre-eclampsia. |
Syndrome characterised by hypertension (≥140/90 mmHg) and proteinuria after 20 weeks gestation |
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Describe how pre-eclampsia is caused by an abnormal placenta. |
Abnormal invasion of trophoblasts into the maternal tissue → spiral arteries do not undergo full physiological change → reduced placental blood flow |
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When and why is chorionic villus sampling (CVS) used? |
When: 10-14 weeks gestation
Why: diagnostic (not screening) check for genetic abnormalities
Chorionic villi have same chromosome complement as foetus
1-2% risk of miscarriage |
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When and why is amniocentesis used? |
When: 14-16 weeks gestation
Why: diagnostic (not screening) check for genetic abnormalities
Samples amniotic fluid which contains fetal cells → cells can be grown in cell culture and fetal chromosomes analyzed Lower miscarriage risk ~ 1% |
