7. Early Embryonic Development - The Pre-embryonic Period Flashcards
What is the blastocyst?
The formation of a cavity.
What is the pre-embryonic period?
The first two weeks of development, formation of morula and then blastocyst and when implantation begins.
Where should implantation happen?
On the posterior uterine wall.
Where is the oocyte released from?
The ovary.
Where does the oocyte get fertilised by the sperm?
In the ampulla of the Fallopian tube.
When does cleavage happen?
30 hours after fertilisation.
What happens in cleavage?
The zygote divides into 2 blastomer ew of equal size, half the size of the original zygote.
What is the zone pellucida?
The glycoprotein shell of the zygote.
What does totipotent mean?
The capacity to become any cell type.
In in vitro fertilisation, when is the morula transferred into the uterus?
After dividing to the 4 or 8 cell stage.
What happens in pre-implantation genetic diagnosis?
A cell is removed from the morula and tested for serious heritable condition prior to transfer of the embryo into the mother.
What is the outer cell mass called and what does it give?
Trophoblast, it gives supporting cells, membrane and the placenta.
What is the inner cell mass called and what does it give?
Embryo blast and it gives the embryo.
Define pleuripotent.
The capacity to become one of many cell types.
What happens in hatching in week 1 of early embryonic development?
The blastocyst hatches from the zona pellucida and now is free to enlarge. It can interact with the uterine surface to implant.
How many cells does the conceptus have when it implants?
107- 8 to make the embryo and 99 to begin development of the fatal membranes and placenta.
Why is week 2 of early embryonic development known as the week of twos?
Two distinct cellular layers energy from the outer cell mass: synctiotrophoblatst and cytotrophoblast, and the inner cell mass becomes the bilaminar disk: epiblast and hypo blast.
What has happened by the end of the 2nd week?
The conceptus has implanted and the embryo, with its two cavities, will be suspended within a supporting sac.
What is the purpose of implantation?
To establish maternal blood flow within the placenta so changes of the embryo from histiotrophic (support from tissues) to haemotrophic (support from maternal blood flow) is supported.
What is meant by the implantation is interstitial?
The uterine epithelium is breached and the conceptus implants within the uterine stroma.
What are four conditions linked to implantation defects?
IUGR (interuterine growth restriction), pre-eclampsia, ectopic pregnancy and placenta praevia.
What is an ectopic pregnancy?
Implantation at another site than the uterine body, often the Fallopian tubes, that can be peritoneal or ovarian and can become a life-threatening emergency.
What is placenta praevia?
Implantation in the lower uterine segment that can cause haemorrhaging in pregnancy and requires a C-section delivery.
What happens on day 9 of early embryonic development?
There is rapid development of synctiotrophoblast, embryonic pole. Also primitive yolk sac is formed, abembryonic pole. The yolk sac membrane is in contact with cytotrophoblast.
What happens on day 11 of early embryonic development?
The primitive yolk sac membrane is pushed away from cytotrophoblast layer by an acellular extraembryonic reticulum. The reticulum later converts to extraembryonic mesoderm by cell migration.
What happens on day 12 of early embryonic development?
The maternal sinusoids are invaded by synctiotrophoblast and the lacunae become continuous with sinusoids. Uteroplacental circulation begins. The uterine stroma prepares for support of the embryo.m
What happens on day 13 of early embryonic development?
Formation of the secondary yolk sac, from pinching off from the primitive yolk sac.
What happens on day 14 of early embryonic development?
Spaces within the extraembryonic mesoderm merge to form the chorionic cavity. The embryo and its cavities are suspended by the connecting stalk.
Why can bleeding around day 14 of early embryonic development be confused with menstrual bleeding?
Because it is a very vascular and invasive process where there is a breach of endometrium.
What is the blastocoele?
The first cavity, formed as a result of compaction.
What is the amniotic sac?
Formed from spaces within the epiblast.
What is the primitive yolk sac?
Formed by hypoblast lining blastocoele.
What is the secondary yolk sac?
Formed within the primitive yolk sac.
What is extraembryonic coleum?
Formed from spaces within extraembryonic reticulum and mesoderm.
What percentage of zygotes are lost in the first 2/3 weeks?
50%
What percentage of diagnosed pregnancies will miscarry?
15%.
What percentage of women will have recurrent miscarriages?
1%.
What is the morula?
When the fertilised oocyte develops into a multicellular ball.
