14 - Placenta Flashcards

1
Q

What day does implanation occur and where does it occur?

A
  • Day 6 after it has hatched from zona pellucida
  • Usually implants on superior body of uterus but can implant lower down or on previous C-section scars that are not viable or not in the uterus
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2
Q

What are some problems with invasion of the conceptus into the endometrial wall?

A

- Too deep: placenta accreata

- Incomplete invasion: miscarriage or placental insufficiency that can lead to preeclampsia

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3
Q

When does the placenta develop and how?

A

- Week 2 before anything else

  • From fetal membranes

- Chorionic sac and amniotic sac separate but then as the amniotic sac enlarges it displaces the chorion and fuses with the chorionic membrane

- Projections around all surfaces of this membrane concentrated into a small disc like space that becomes the placenta

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4
Q

What does implanation achieve?

A
  • Basic unit of exchange
  • Anchor the placenta
  • Establish maternal blood flow
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5
Q

What are chorionic villi?

A
  • Villi that sprout from the chorion membrane

- Inner connective tissue core, where fetal vessels can form, and outer layer of syncytiotrophoblasts

  • Maternal blood vessels surround villi so exchange can occur but mixing of circulations never
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6
Q

How do the chorionic villi change over pregnancy?

A

1st trimester: barrier between maternal and fetal blood vessels thick. Full layers of cytotrophoblasts and syncytiotrophoblasts

3rd trimester: barrier less, becomes one layer of trophoblast by reducing cytotrophoblasts

Margination of fetal capillaries and loss of trophoblasts

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7
Q

How is the degree of invasion of the conceptus controlled?

A

Decidua = endometrial becomes specialised through decidualisation

If implantation in correct place but decidual reaction is suboptimal can lead to complications like miscarriage, infertility or placental insufficiency leading to pre-eclampsia

Implanation in incorrect place then no decidual reaction so ectopic

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8
Q

Label the gross morphology of the placenta.

A
  • Amnion on outside with chorion vessels underneath
  • Need to check placenta for cotyledons to check none of them have fallen out and can cause post partum haemorraghe
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9
Q

What are the main blood vessels exchanging the placenta and how are they arranged?

A
  • Endometrial arteries bathe the villi
  • Paired umbilical arteries carry waste products to villi
  • Single umbilical vein takes oxygen and nutrients to fetus
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10
Q

What is the endocrine function of the placenta?

A
  • hCG from syncytiotrophoblasts maintain corpus luteum in first trimester. urine and blood tests
  • Steroid hormones made to take over corpus luteum and produce enough oestrogen and progesterone to keep body in pregnant state
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11
Q

Why may someone have high levels of hCG in their blood?

A
  • Pregnancy specific, from syncytiotrophoblasts
  • Molar pregnancy
  • Testicular cancer
  • Choriocarcinoma
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12
Q

How do placenta hormones change the metabolic state of the mother?

A
  • Progesterone: increases appetite to allow increased fat deposition to support fetus and breast feeding

- Human Placental Lactogen (hCS): creates diabetogenetic state by causing insulin resistance to mother so more glucose availability for fetus

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13
Q

How does transport across the placenta occur?

A

- Simple diffusion: water, gases, electrolytes

- Facilitated diffusion: glucose

- Active transport: aa’s, Fe, vitamins

- Receptor mediated endocytosis: IgG’s

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14
Q

How does gas exchange occurs across the placenta?

A
  • Simple diffusion
  • Flow limited and fetal O2 stores are low so adequate flow essential
  • Can have fetal distress (hypoxia) in labour contractions as they compress uteroplacental circulation
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15
Q

How does the baby confer immunity?

A
  • IgG antibodies from mother can pass across placenta via receptor mediated endocytosis
  • Protects baby
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16
Q

What is rhesus disease of the newborn?

A
  • Haemolytic disorder that can occur due to being able to transfer across placenta. Not common as screened for now
  • Causes baby jaundice and anaemia
17
Q

When do teratogens cause the greatest effect in pregnancy?

A
  • Preembryonic: fatal

- Embryonic (3-6 weeks): sensitive as body systems developing

- Fetal (9-36 weeks): +/- sensitive apart from CNS

18
Q

What are some harmful substances to the fetus?

A
  • Thalidomide
  • Alcohol (FAS and ARND)
  • Therapeutic drugs (antiepileptic, warfarin, ACEi)
  • Smoking (low birth weight)
  • Drugs (dependency)
19
Q

What are some dangerous infections to have in pregnancy and why?

A

Mother is in immunocompromised state so infections more serious, need to check mother’s immunisation status. Poor pregnancy outcomes