Implantation Flashcards
What does compaction in morula lead to in the development of the blastocyst
POlarity and asymmetric division that results in daughter cells having different properties from each other
What does the trophectoderm form in a blastocyst and what is it
Forms placenta
It is a layer of trophoblast cells
What does the inner cell mass in a blastocyst form
Embryo
What does the zona pellucida do
Prevents blastomeres falling apart during early cleavage
What are the 3 phases of implantation
Attachment
Adherence
Invasion
When does attachment of blastocyst to endometrium occur
Only in the Luteal phase of the endometrium when it can provide nutrition (Uterine milk)
Once attached/implanted, how does the blastocyst obtain nutrients and what is this process called
Diffusion
Histiotrophic Nutrition
What is progesterone and oestrogen like in luteal phase
High
What do the high progesterone and oestrogen cause the epithelial cells lining the endometrium to do and what is this called
Lose surface glycocalyx
Lose anionic charges
Flatten their microvilli
Have thin mucin coat
This is called Primary Decidualisation
What is the implantation window
It is 2-3 day period during mid luteal phase where hatched blastocyst can adhere during this window
How does the blastocyst communicate to mother that it is still there so she doesn’t; get rid of it
Long range communication which alters the pituitary ovarian axis
1) Trophoblast cells secrete hCG which is an analogue of LH
2) hCG carried to ovary and binds to LH receptors on granulose cells of corpus lute which continues to produce progesterone and suppresses luteolysis
3) This prolongs life of corpus lute
4) Corpus luteum continues to produce progesterone up to 4 months. Thereafter, placental production is high enough to take over
5) Endometrium remains in progesterone dominated secretory phase throughout gestation
What does adhesion between trophoblast and epithelial cells of endometrium lead to and what is this called
Why does this occur
changes in stroma in the endometrium. This spreads to areas surrounding the blastocyst and along the uterus
This is called Secondary Decidualisation
-Happens because of high progesterone and hCG
What does the ‘Secondary Decidualisation’ spread to create
3 Decidual layers
Decidua basalis (endometrium underlying the conceptus. This shows the highest changes as this is where the conceptus needs to burrow into. This is called the basal plate of the placenta)
Decidua capsularis (superficial portion overlying the conceptus)
Decidua parietali (remaining uterine mucosa)
How does the endometrium enhance attachment to the blastocyst
Produces LIP which acts as a ‘come hither’ messenger
Downregulates anti-adhesive cell surface mucin MUC1 which normally acts as a ‘go away’ molecular message
Epithelial cells adjacent to the blastocyst produce heparin binding EGF-like growth factors and HSPG
What may high levels of MUC1 be behind
Misscarriages