Early Embryology Flashcards
Development of human being:
Fertilisation
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Single cell
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Ball of cells
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Cavities + two layered disc
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Three layered disc with middle layer
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Segments in middle layer + tubes form from two outer layers
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Fully formed bodyWhere does fertilisation occur?
Ampulla of uterine tube within 12 hours of ovulation
What happens in fertilisation?
Reduction divisions (oocyte) completed
Restores diploid number of chromosomes (46)
Genetic sex determined
What type of cells are sperm and ovum?
Haploid (23 chromosomes)
What happened within 36 hours of fertilisation?
Initiation of cleavage
What essentially is the acrosome reaction?
Regulated exocytosis
Enables penetration of zona pellucida
How is acrosome reaction triggered?
Sperm penetrates corona radiata (hyaluronidase)
Interacts with ZP3 receptor
What happens during acrosome reaction?
Sperm digests zona pellucida
Sperm and oocyte membrane fusion
What happens after sperm fuses with oocyte?
Completion of oocyte meiosis
Release of nucleus into oocyte cytoplasm
What happens to prevent second entry of sperm into oocyte?
Cortical granules release content to degrade ZP3
Increase in oocyte membrane negative charge
What happens in 1st week of development?
Ovulation to implantation
What happens in donation of healthy mitochondria?
Parent’s nucleus removed and kept
Donor nucleus removed and destroyed
Parent’s nucleus placed inside donor egg
What happens to zona pellucida in first week of development?
Remains intact
Mitosis in first week of development:
Maternal and paternal chromosomes line up on spindle equator
Chromatids separate
What doesn’t happen in first week of development?
Cell growth - as only division in same volume
When does initiation of cleavage occur?
Within 36 hours of fertilisation
Early cleavage:
Cell division without growth (inside zona pellucida)
When does compaction cleavage begin?
At 8 cells - central cells linked by gap junctions
Become more like a homogenous ball
Anterior/posterior axis of embryo established
What’s a Morula?
16+ cells
Inner and outer layers
What happens to morula?
Transported along uterine tube to uterus
Zona pellucida disappears
What happens to outer cells on morula?
Divide to become trophectoderm (trophoblast) and inner cells (inner cell mass)
What happens at 4.5 days?
Cavities form in inner cell mass
Blastocyst unattached to uterus
What’s a blastocyst?
Trophoblast and inner cell mass
What happens at 5-6 days in genetic testing?
Trophectoderm sampled
What happens at 5.5 - 6 days?
Blastocyst binds to uterus epithelium
Embryonic pole attaches
How does blastocyst bind to uterus wall?
Down regulation of anti-adhesion molecule MUC-1
Allows binding via selectins to glyco-compartments on epithelial cells (uterus)
What molecules are involved in binding of blastocyst to uterine wall?
Integrins, laminin and fibronectin
What happens at 6-7 days?
Implantation of blastocyst starts
What happens during implantation of blastocyst?
Trophoblast becomes invasive
Scynctiotrophoblast multinucleate synctium invades via metalloproteases
What does blastocyst implantation cause?
Immunosuppressive of host/graft and graft/host reactions
What happens on day 8?
More embedding of blastocyst into uterine wall
What happens to trophoblast on day 8?
Divides into synctiotrophoblast and cytotrophoblast
What happens to embryo on day 8?
Two layers form - epiblast and hypoblast
Amniotic cavity (space)begins to form within epiblast.
What coats blastocyst cavity?
Hypoblast cells - on day 9
What becomes primary yolk sac?
Blastocyst cavity
What happens on day 9?
Form primary yolk sac
Spaces develop within synctiotrophoblast
Formation of amniotic cavity
What is formed deep to trophoblast following day 9?
Extraembryonic mesoderm
Does the embryonic disc have layers?
Two layers
What happens on days 11-12?
Blastocyst burrows completely into endometrium
Synctiotrophoblast cells erode through walls of large maternal capillaries
What causes primitive placenta circulation?
Days 11-12
Synctiotrophoblast cells erode through large maternal capillary walls + bleed into spaces
What new layer is formed in days 11-12?
Between yolk sac and cytotrophoblast
What are spaces formed in, in days 11-12?
Extra embryonic mesoderm
What’s the chronic in cavity formed by?
Fusion of spaces in extra embryonic mesoderm (days 11-12)
What two layers develop in trophoblast at the end of week 2?
Synctiotrophoblast
Cytotrophoblast
What 2 layers form in the inner cell mass at the end of week 2?
Epiblast - ectoderm
Hypoblast - endoderm
What two cavities form at the end of week 2?
Amniotic cavity
Chorionic cavity
What’s preeclampsia?
Features maternal hypertension and proteinuria after 20 weeks
Where’s the most common site of ectopic pregnancy?
Ampulla - results in tube rupture + blood loss
What environmental causes of malformations are there?
Drugs/chemicals
Infectious agents
Ionising radiation
What determines dorsal-ventral axes in embryo?
Oocyte - but unclear mechanisms
What determines left right axes in embryo?
Cilia movement (tend to be one direction) in node
What axes are there in the embryo?
Dorsal-ventral
Left-right
Rostral caudal
