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
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
- involves decrease in Oct4 with an associated increase in Cdx2
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
4
Q
Where does normal human blastocyst implantation occur?
A
In the anterior or posterior wall of the body of the uterus
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