Preimplantation of embyo Flashcards
If its a mammal, embryo implants
Whats so significant about it
- Blastomere division is not synchronous (not at same time)
- Mitosis is slow
- there is compaction stage
- Blastula= blastocyst
- Blastocyst hatches then implants
- Regulative development ( No morphogens)
What type of eggs are mammalian eggs compared to frog eggs
Isolecithal- even distribution of yolk
Frog eggs are telolecithal ( vegetal pole more yolk than animal)
What type of cleavage does mammals do
Holoblastic= full cleaavage of egg and yolk (like frogs)
Cleavage is rotational, asynchronous, 24 hours per cycle.
1st cleavge=meridional
2nd= meridional and the other equatorially
What is the first morphological event in the preimplantation development
COMPACTION
What is compaction
Transfoms embryo to loose cluster of cells to tight packed mass
Blastomeres start to look different here from each other
With compaction , what else is established
Intracellular polarization
What does polarization involve
Some peripheral cells make 1 polarized and 1 non polarized cell
NON POL= forms inner cell mass-embryo
POL= stays at periphery and becomes trophoectoderm
Why is trophoectoderm important? what do they dfferentiate into
Differentiate into large trophoblasts for the placenta
Imp for hatching and cavitation of blastocyst
What do the polar/mural trophoectoderm cells do
polar-contact the inner cell mass and proliferate
Mural- surrounds blastocoel and differentiates into large trophoblast cells
Why are trophoectoderm polyploid
endoreplication - replication with no mitosis
How does cavitation occur (64 cell stage)
- intracellular vaculoles appear first
- Eventually these r drained into inner cell mass the forms blastocoel
- For fluid to accumulate you need tight sealed trophoectoderm layer- sealing done by non contrac=tile actin rings- expands to reach tight junctions and adherens
What is involved in blastocyst hatching
Blastocyst expnads due to liquid accumulation in blastocoel
When burst, it becomes free of the zona pellucida
5-6th day
NOW IT CAN IMPLANT
What are zona breaker cells
speazilied trophovblast cells that have secretory vesicles to open the zona pellucida
Where does embryo implant
Endometrium
At implantation, what does the trophoectoderm produce
Chorion
Forms vili and makes maternal pacenta nutrion
Produce hormones
WHat if implantation ocurrs at the wrong place
Ectopic pregnancy
Zona pellucida normally prevents embryo attaching to wall of fallopian tube but this could go wrong
Other than zygote what else can initiate embyonic development
blastomeres are totipotent
Until mitosis promoting factors start
What can totipotent cells turn into that pluripotent cannot
extraembryonic tissue like placenta
OOplasmic segregation vs signal transdiction
OOplasmic is intrinsic with morphogens
transduction is extrinsic= signal interacts with receptor, sends cascade (second messengers) to nucleus and influence transcription factors for gene expression
What are the benefits of regulative development
DOES NOT DEPEND ON MORPHOGESN
DEPENDS ON INTERACTIONS WITH O|THER CELLS
What is eveidence of regulation
Identical twins
More than 1 embryo leads to twins. But always may not
Chimera
The 2 blastocysts fuse and form chimeric embryo
Can have diff sex organs, bloody types etc
MECHANISM OF PREIMPLANTATION
- 16 cell stage= morula
- Blastocyst forms, then blastocoel (64 cells)
- From peripheral cells forms:
Inner cells= inner cell mass of pluriopoitent cells
Peripheral cells=trophoectoderm differentiates into
trophoblast cells - Accumulation of fluid in blastocoel then bursting = hatching
free of ZP (6th day) - Polar trophoectoderm= proliferate
Mural trophoectoderm= differentiate into trophoblast cells - Implantation with trophoectoderm makes chorion, develops villi for feto maternal interactions and produces hormones
