Physiology of Reproduction 4 Flashcards
Day 1 fertilisation
4-7 hours after fusion, the two sets of haploid chromosomes form the female and male pronucleus.
They are the same size and contains nucleoli.
Syngamy
The male and female pronucleus migrate to centre
The haploid chromosomes make DNA in prep for the first mitotic division.
Pronuclear membrane breaks down
Mitotic spindle forms
46 chromosomes organise at spindle equator
What day is cleavage?
Day 2
How could diploid or triploid mosaics occur?
if one or more of the pronuclei fails to decondense and move in to one of the blastomere.
What does the zona pellucida do?
Maintains micro-environment for embryo until it hatches at the blastocyst stage.
Where does fusion of sperm and egg occur?
Ampulla
Where does the sperm head bind to?
Glycoproteins (receptors) on the zona pellucida (ZP3)
How does binding off sperm to zona pellucida happen?
Acrosome reaction = zona pellucida is digested by enzymes
Why is important the membrane potential of the egg cell is changed?
To prevent entry of other sperm (polyspermy)
How is the membrane potential of the egg changed?
Exocytosis of vesicles which contain enzymes that inactivate ZP3 (receptors on zona pellucida)
What is the pronuclei?
The 2 sets of haploid chromosomes (equal in size and contain nucleoli)
They migrate to centre of cell and fuse.
DNA replication occurs ready for meiotic division.
Mitosis.
Where does cleavage happen?
Zygote in fallopian tube
What hormone increases smooth muscle relaxation of fallopian tube to allow zygote to pass through?
Progesterone
What type of cell does the zygote divide into
Zygote divides into many totipotent cells
What type of cell does the zygote divide into?
Totipotent cells
What happens in day 4?
Compaction
8-cell uncompacted morula becomes 8-cell compacted morula
What does compaction involve?
Cells flatten and maximise space
Tight junctions form
Polarisation of outer cells
Allow rapid differentiation.
What day does cavitation and differentiation occur?
Day 5
What happens during cavitation?
The fluid filled cavity expands and forms blastocysts
More than 80 cells.
Loses totipotency.
outer cell layer (throphoblast) and inner cell mass with fluid filled cavity in the middle.
What is the outer cell layer of blastocysts called?
Throphoblast
What day/s does expansion occur
Day 5-6
What happens during expansion?
Cavity expands further
Zona pellucida thins
From what day does hatching occur?
Day 6
What happens during hatching?
Blastocyst expands, embryo out of zona pellucida.
Essential for implantation.
What day does implantation occur?
Day 7
For how long do the endometrial cells provide the metabolic fuel needed for early growth?
First 5 weeks, whilst foetal heart develops
When does apposition occur?
Day 9
What is apposition?
Hatched blastocyst orientates via embryonic pole
Synchronises with endometrium
What is attachment?
Integrins between endometrial endothelium and trophoblast cells.
What 2 layers does the trophoblast layer split into during differentiation?
Cytotrophoblast and synctiotrophoblast
