Preimplantation development

Question 1

when does compaction occur?

Answer 1

at the 8 cell stage

Question 2

what happens during compaction?

Answer 2

E-cadherin is redistributed in each blastomere so it is localised to all the cell contact sites
Causing cells to flattern and adhere to one another
Concurrent onset of cell polarity with loss of microvilli from contact sites - gap and tight junctional complees form

Question 3

what is compaction mediated by?

Answer 3

redistribution of e-cadherin (a member of the Ca2+ dependent adhesion molecules)

Question 4

what significant division occurs between the 8 cell compaction and 16 cell morula?

Answer 4

differential cell division whereby cells inheriting the apical domain of parental 8 cell balstomeres will from part of the trophectoderm at the 32 cell stage
whereas cell inheriting the basal domain, will remain on the interior and give rise to the inner cell mass

Question 5

what is the second morphological event of preimplantation development that results in the first two lineages of development and what are they?

Answer 5

Cavitation
(blastocyst formation)
at the 32 cell stage

Question 6

whats the point of tight junctions in the blastocyst?

Answer 6

provides impermeable seal allowing fluid to accumulate, regulates paracellular transport and contributes to a polarisation of the distribution of the Na+ , K+ , ATPase.

Question 7

what features are present on the basal membrane of the blastocyst?

Answer 7

Basal membranes contain the sodium potassium pump (Na+ , K+ , ATPase). Transports ions across the TE resulting in the vectorial transport of water into the blastocoel

Question 8

what are the steps the egg goes through from ovary release to implantation?

Answer 8

At ovulation egg is released from ovaryl to the ampulla region of the fallopian tube, fimbrulae help it move through the tube.
It continues to develop as it moves through the tube.
Embryos all enclosed in zona pellucida coat, prevents it implanting as it moves along the embryo tube
Compaction occurs at the eight cell stage, to get a morula. Becomes a blastocyst when you can see the blastocyst cavity forming. It is at the blastocyst stage when it reaches and implants into the uterus.
In the expanding blastocyst you see the first tow cell lineages; trophoblasts and the inner cell mass.
Fluid accumulates and it continues to expand. Then you get a hatching blastocyst when the zona pellucida breaks and the blastocyst get escape to implant