implantation Flashcards

1
Q

hatching of the blastocyst requires

A
  • proteolytic enzymes secreted from the trophectoderm and possibly from uterine secretions
  • to dissolve a hole in the ZP for the blastocyst to squeeze out
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2
Q

why is human implantation called “invasive”

A

conceptus breaks through the surface epithelium to invade underlying uterine stroma

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3
Q

what is placenta praevia

A

(normally implants close to top)
- implants on/close to cervix
- restricts placental growth so is associated with antepartum haemorrhage

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4
Q

can the embryo implant at any time?

A
  • majority of time, uterine epithelium is non-receptive
  • receptive during progesterone dominant phase
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5
Q

role of oestrogen and progesterone in implantation

A
  • both required to prime uterine lining
  • oestrogen needed to prepare conceptus
    (known from rat experiments & ovariectomy after implantation)
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6
Q

properties of non-receptive endometrium

A
  • epithelial cells resistant to embryo adhesion
  • cells have a thick mucin (MUC1) glycoprotein coat, long microvilli & negative surface charge
  • high level of PG receptor expression to prepare for blastocyst binding
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7
Q

properties of receptive endometrium

A
  • blastocysts adhere to thinner mucin coat, no negative charge, LIF = “come here”, shorted microvilli
  • pinopodes allows absorption of uterine fluid so less uterine cavity vol so adhere to uterus
  • decrease in PR receptors
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8
Q

describe apposition

A
  • blastocyst approaches and interacts with uterine epithelium
  • L-selectin binds to ligand in epithelium, which promotes secretion of hCG by trophoblast, which signals to epithelium to secrete trophinin and break down MUC1 glycocalyx (so trophoblast can interact better)
  • allows LIF signalling
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9
Q

describe LIF signalling

A
  • causes upregulation of HB-EGF on uterine epithelium which binds to HSPG on trophoectoderm and ErB on the trophoblast > release of prostaglandins, decidualisation
  • induces expression of adhesion molecules, e.g. integrin, on both surfaces: OPN induces integrin on trophoblast
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10
Q

describe message exchange in adhesion and invasion

A
  • containment & control to keep trophoblast in check (TIMPs)
  • incitement & encouragement to promote invasive events (MMPs)
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11
Q

describe the decidual reaction

A
  1. uterine epithelial cells start signalling to underlying stroma that invasion is imminent
  2. endometrium becomes nutrient packed, highly vascular tissue called decidua - involves PGs
  3. maternal stromal cells of endometrium > maternal decidual cells (spindly > large and round because lipids and glycogen)
  4. decidual cells secrete cytokines, incl IGF binding proteins and prolactin, that aid placental growth
  5. increased vascular permeability and angiogenesis
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12
Q

three regions of the decidua

A
  1. decidua basalis: closest to myometrium
  2. capsularis: covers protruding side of conceptus; will disintegrate over time
  3. parietalis: remainder of decidua
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13
Q

why is the endometrial lining newly developed with each cycle

A

decidual cells cannot dedifferentiate into stromal cells

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14
Q

how does the conceptus prevent shedding

A
  • secretes hCG
  • maintains corpus luteum so progesterone stays high & cannot start a new menstrual cycle
  • by 10w, placenta secretes enough progesterone
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