Implantation 2 Flashcards

Describe the process of normal implantation.

1
Q

What is the fetal conbribution of the normal process of implantation?

A
  • Trophectoderm differentiation during blastogenesis
  • After fertilization, zygote undergoes cell divisions to produce smaller cells called blastomeres
  • Compaction (tight aligning of cells) results in the inner cell mass and outer cells differentiate into trophectoderm that eventually become the trophoblast and placenta
  • Space develops in morula between inner and outer cells to make the blastocyst and zona pellucida disappears
  • Blastocyst rolls along uterine cavity and orients the embryonic pole to face the endometrial lining (usually)
  • Embryo then attaches to the uterine wall at day 5-6 post-fertilization
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2
Q

Describe the molecular regulation of the first true differentiation event in human development.

A
  • Formation of the trophectoderm from the inner cell mass
  • Regulated at the molecular level by a switch resulting in trophectoderm rather than inner cell mass
    • involves decrease in Oct4 with an associated increase in Cdx2
      • Oct4 maintains pluripotency
      • Cdx2 acts as a molecular switch to promote trophoectoderm differentiation
    • Tead4 is upsream of Cdx2
    • Sox2 and Gata3 also important
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3
Q

What is the maternal contribution to implantation?

A
  • Proper decidualization is very important
    • Estrogen priming
    • Early steps induced by progesterone
      • stromal cells become decidualized and take on a different histologic appearance (larger with lipid and glycogen vacuoles) and altered function
  • Implantation occurs in the endometrium in the secretory phase
  • Decidua impedes movement of invasive trophoblast by forming physical barier and cytokines that promote attachment rather than invasion
  • Early decidua also provides nutirents to developing embryo and aids in immune tolerance
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4
Q

Where does normal human blastocyst implantation occur?

A

In the anterior or posterior wall of the body of the uterus

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5
Q

What are the molecular mediators of blastocyst attachment?

A
  • L-selectin on the trophoblast surface interacts with carbohydrate receptors on the uterine epithelium
  • Integrins and laminin facilitate attachemnt
  • Fibronectin regulates migration
  • Trophoblast differentiation signals also part of the process
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