Pre-embryonic Period Flashcards
What are the main events in the first two weeks of development?
Cleavage and formation of the morula
Compaction and formation of the blastocyst
Implantation begins
How long are the pre-embryonic, embryonic and post-embryonic periods?
Pre: weeks 1-3
Embryonic: weeks 3-8
Foetal: weeks 9-38
Describe the events of fertilisation
Oocyte released from the ovary
Travels along the Fallopian tube
Fertilised by sperm in the ampulla to form a zygote
Where is the idea site for implantation?
Posterior uterine wall
How long is an oocyte and a sperm viable for?
Oocyte: 1 day
Sperm: 3 days
When does cleavage begin and what does it result in?
30 hours tater fertilisation
2 blastomeres which make up the morula
In the morula, what is the differentiation status of the cells?
Totipotent
During IVF, when is the morula transferred into the uterus?
After it has divided to the 4 or 8 cell stage
What is PGD?
Pre-implantation genetic diagnosis
When a cell is removed from the morula and tested for serious heritable conditions prior to transfer of the embryo to the mothers
Done in IVF
What does compaction produce?
A blastocyst
Structure of a blastocyst?
Blastocyst cavity
Inner cell mass (embryoblast)
Outer cell mass (trophoblast)
Surrounded by the zona pellucida
What is the differentiation status of the cells in the blastocyst?
Pluripotent
What happens in hatching?
The blastocyst hatches from the zona pellucida so that it is no longer constrained and free to enlarge
What does hatching allow?
The blastocyst is free to enlarge
Can now interact with the uterine surface to implant
How many cells are there at the beginning of implantation? How many are for which functions?
107 cells
8 to make the embryo
99 to begin development of the fetal membranes
What happens to the outer cell mass in week 2?
Forms two distinct cellular layers
- syncytiotrophoblast
- cytotrophoblast
What happens to the inner cell mass in week 2?
Becomes the bilaminar disc
- epiblast
- hypoblast
List some conditions linked to implantation defects
IUGR
Pre-eclampsia
Ectopic pregnancy
Placenta praevia
What is an ectopic pregnancy?
When there is implantation at a site other than the uterine body
What is placenta praevia?
When there is implantation in the lower uterine segment
What can placenta praevia lead to?
Haemorrhage in pregnancy
Requires C-section delivery
What is the primitive yolk sac produced from?
The blastocyst cavity
What happens during implantation?
Syncytiotrophoblast cells invade the epithelium and underlying endometrial stroma with the help of proteolytic enzymes.
What are the effects of implantation?
Establishes maternal blood flow within the placenta
Establishes basic structural unir of materno-fetal exchange
How does the secondary yolk sac form?
Pinches off from the primitive yolk sac
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 from?
The hypoblast lining the blastocoele
What is the chorionic cavity/extra embryonic coelom formed from?
Spaces within the extraembryonic reticulum and mesoderm
