Extraembryonic membranes Flashcards
What are the 4 extraembryonic membranes in placental mammals?
What are the roles of EEMs?
- Transfer of nutrients in and breakdown products out
- Physically protect the embryo
- Protect the embryo from toxins and hormonal changes
- Protect the embryo from temperature changes
- Protect from maternal immune system
- Allow growth (not pressing on the embryo)
- Cellular differentiation – Gonadal stem cells, haematopoietic stem cells
- Drive hormonal changes:
- Signal to mother pregnancy is occurring (hCG)
- Maintain uterine relaxations and secretions (progesterone)
- End pregnancy and Induce parturition (oestrogen- CRH)
- hGC- maintains CL and later runs proesterone from placenta
- (chorio-allantois and yolk sac)
Role of progesterone + 17beta oestradiol in uterine growth and implantation
What was the first EEM to appear?
Chorion the first membrane to appear – foetal side formed from the trophectoderm
Forms the chorionic membrane from the highly motile trophoblast cells which migrate into the uterine wall (endometrium)
Tell me the two placeta that form and due to what?
The foetal placenta will form from these cells -
- The allantois fuses with this and mesoderm migrates in from the embryo itself (forms blood vessels) —chorio- allantoic placenta
The maternal placenta forms usually at the upper surface of the uterus (more later)
When trophoblasts enter the maternal tissue they differentiate into 2 layers, what are these layers?
Trophoblast when they enter the maternal tissue differentiate to 2 layers
- Inner Cytotrophoblasts
- Outer Syncytiotrophobasts
In time some of the Cytotrophoblasts lining the cavity form Giant cells which help remodel blood vessels
Chorion
Chorion
What is the cytotrophoblast?
The cytotrophoblast is the trophoblastic stem cell
What are the four lineages of the cytotrophoblast?
Forms four lineages
- The fusion lineage -Syncytiotrophoblast
- The invasive lineage interstitial Cytotrophoblast
Then later…
- Through endoreduplication- TrophoblastGiant Cells
- Structural Spongiotrophoblasts
What does the Syncytiotrophoblast control?
Syncytiotrophoblasts control both maternal adaptive and innate immunity, Physical separation
What does the Syncytiotrophoblast express, block and produce?
- Express cell surface non-classical MHCI molecules (C-E-G) inhibit NK cells, suppress CTL activity and upregulate the local CD4’ Treg cell differentiation.
- Block innate immunity via the modification of neutrophil function and NET formation.
- Produce hCG- signal to mother pregnancy has started
- Not HLA-A and HLA-B, but atypical MHC class I isotypes HLA-E and HLA-G, as well as HLA-C
What can the LH not support after ovulation?
LH (from pituitary reduces) cannot support Corpus Luteum (CL) after ovulation.
Tell me about the co-dependence of the corpus luteum and the embryo
- Corpus luteum needs embryo to survive
- Embryo needs corpus luteum to survive
- In absence of embryo- no hCG produced, CL will die (10-14 days after ovulation )
What is the hormone of pregnancy?
Progesterone
Tell me the roles of progesterone
- Blocks further follicle development and ovulation (blocks FSH and LH)- so single embryo (or one timed wave of ovulation).
- Barrier at cervix for sperm entry- mucus plug stops entry of microorganisms. Cervical plug.
- Induces uterine endometrium to make a nutrient-rich food source for embryo (secretory phase- needs estrogen too).
- Keeps uterine myometrium ‘quiescent’
- Induces breast tissue growth ready for lactation
What is progesterone made by?
Progesterone made by placenta later in pregnancy between 4-7 weeks
Tell me the formation of the placenta at human E14?
Tell me the formation of the placenta at human E16
Tell me the formation of the placenta at human E20
Tell me the formation of the human placenta E14- E20
- At human E14 Cytotrophoblasts grow out into the endometrium increasing the contact surface the primary chorionic villus
- At human E16 Extra-embryonic mesoderm grows out into the primary villi increasing the contact surface further - the secondary chorionic villus
- At human E20 vessels form in the secondary villi mesoderm– this forms the tertiary chorionic villus
What are trophoblast giant cells and what their role?
- Trophoblast giant cells.
- highly polyploid (switched from a mitotic to endoreduplicative cell)
- Like metastatic tumour cells, they breach basement membranes and invade deeply into the maternal decidualized uterine stroma.
Tell me the properties of trophoblast giant cells
Highly angiogenic and vasodilatory properties, remodel arterial walls, enable them to redirect maternal blood flow towards the implantation site.
What are the trophoblast giant cell subtypes?
What are the trophoblast giant cell characteristics?
Maternal vessel entry and placental development doesn’t occur over the whole chorion Villus formation is biased to the upper region – decidua basalis/ placentalis