Lect 2 Flashcards
When does a blastomeres become a morula?
When 8 or more cells, compaction occurs! Usually Day 4
What are the events in the pre- embryonic week 1?
There are 5
- ) cleavage : mitioc divisions - blastomeres
- ) compaction: tightening to form morula
- ) cavitation: uterin fluid in morula - blastocyst
- ) hatching : blastocyst hatches from ZP
- ) implantation : blastocyst implants in endometrium of uterin wall
When does implantation occur?
Day 6
Explain cleavage
Repeated cell divisions ( zygote/ polar bodies) 2 blastomeres continues until 16- morula compaction stage
When is nondisjunction less sever?
During week One of pre embryonic stage! Called mosaicism
At what stage does an inner and outer cell mass form?
Compaction
What cells form from the inner cell mass?
Inner cell mass - embryoblast (form embryo foetus and amnion) - epiblast and hypo blast
What originates from the outer cell mass?
Outer cell mass- trophoblast - cytotrophoblast and synctiotrophoblast ( form placenta and chorion)
When end has the embryoblast attached?
Embryonic pole!
Which end is the abembryonic pole?
Opposite the embryoblast cells
Which cells attach to the uterine wall during implantation?
Trophoblast: day 6
Where do the nutrients during implantation come from?
Uterine gland secretions in endometrium getting broken down by synctiotrophoblast
What events occur during week 2?
Week 2 is the pre embryonic stage:
- ) Implantation is complete! - UTERAPLCENTAL CIRCULATION
- ) Bilaminar Disc - embryoblast differentiates
What cells creat the Bilaminar disc?
Embryoblast
When is Uteroplacental circulation established?
Week 2 of pre embryonic period
After implantation how does the cell type used for implantation change?
Trophoblast then become either cytotrophoblast or synctiotrophoblast ( erode uterine wall and blood vessels)
When does nutrition change from uterin gland secretions to Uteroplacental circulation ?
Uterin gland secretions during implantation, once completed week 2 begins Uteroplacental circulation
When can pregnancy be detected?
Day 8 from the hCG secreted by Sybctiotrophoblast
What is ectopic pregnancy?
When implantation is outside the uterus, usually uterine wall. If further down can cause placental Previa obstructing the cervix. Fixed with c section
What is a molar pregnancy?
Trophoblast implants, but embryoblast is absent or incomplete! ( no embryoblast, no epiblast or no hypoblast : all of which develope the embryo/ foetus and amnion) …yields a tumour HYDATIDIFORM mole ..give hCG from synctiotrophoblast so + preggers test
What is the bilaminar disc?
Embryoblast lamination to give rise to —- hypoblast (line blastocyst cavity which develops into primary yolk sac ) and epiblast ( line amniotic cavity)
When does the blastocyst cavity become the primary yolk sac
Week 2 of pre embryonic period
What cavity do the hypoblast form?
Hypoblast from blastocyst cavity- which will turn into the primary yolk sac! ( epiblast form amniotic cavity)
When does the extra embryonic cavity form?
Week two, adjacent to the hypoblast ( that form the blastocyst cavity) the Extraemryonic mesoderm will form spaces and slowly enlarge to form Extraemryonic cavity! ( cavity outlines the cytotrophoblast and turns the pYS into a secondary yolk sack! And developers an exocoelomic cyst
What is the chorionic cavity?
Also known as the Extraemryonic cavity! Lined by the Extraemryonic mesoderm.
Chorion includes : cytotrophoblast, synctiotrophoblast and EM
