Embryology: Fertilisation to Trilaminar Flashcards
during fertilisation what does sperm bind to
the zona pellucida glycoprotein (ZPG3)
when sperm binds to ZPG3 what happens
it releases digestive enzymes form the sperm head and digests its way into the cell
when the egg and sperm plasma membranes fuse what happens
sperm contents enter the egg
sperm entry into egg triggers 2 things:
- completion of meiosis 2
- oocyte release of cortical granules
function of cortical granules
kill off other sperm do avoid polyspermy
during cleavage what happens
zygote undergoes mitotic division and subdivides the egg into smaller daughter cells
what are the smaller daughter cells produced in cleavage called
blastomeres
how many blastomere cells are totipotent
up to 8
mosaicism
2+ cell lines with different chromosome complements
mitotic non-disjunction
daughter cells have irregular chromosome numbers and can occur in early division of zygote
what surrounds blastomeres
zona pellucida (ZP)
how do cells in blastomeres maximise space
come in close contact with one another and form cell junctions
what do outer cells in close contact with the zona pellucida form
extensive gap junctions
when blastocysts form gap junctions with the ZP what enters
fluid through ZP
what happens during blastocyst hatching
inner cell mass hatches out ZP leaving it behind and the embryo interacts directly with the endometrial lining for implantation
embryoblast
inner cell mass of blastocysts that also consists of amnion and yolk sac
when and where does implantation typically occur
day 6 on posterior/anterior uterine wall
summarise week 1 of fertilisation
- day 1 - egg enters tube and is fertilised - DNA duplication begins
- day 3 - blastocyst enters uterus
- day 5.5-6 - implantation occurs
when does the trophoblast divide
day 7.5
what does the trophoblast divide into
- cytotrophoblast (inner layer)
- synctiotrophoblast (outer layer)
what does the syncytiotrophoblast do
produce the human chorionic gonadotropin
after trophoblast division what does the embryo do
organise into 2 cell layers and the amniotic cavity begins to form
what two layers does the embryo first divide into and what surface do these form
- epiblast (dorsal)
- hypoblast (ventral)
after the embryo divides into 2 layers, what 2 cavities begin to form and from which layer do they form from
- amniotic cavity (epiblast)
- primitive yolk sac (hypoblast)
after the formation of the amniotic cavity and yolk sac what is complete on what day
implantation, day 9
what closes off implantation
fibrin coagulum
where and what forms lacunae
uniting vacuoles in the syncytiotrophoblast
when is uteroplacental circulation established
day 12
where does maternal blood flow into
lacunae
on day 12 what develops (and eventually degenerates)
extraembryonic mesoderm
what does the extraembryonic mesoderm form
chorionic cavity
on day 13 what further develps
chorionic cavity, connecting stalk present
what does the connecting stalk later develop into
umbilical cord
what and when is the definitive (secondary) yolk sac formed
day 13, second wave of hypoblast cell migrate
where is the amniotic cavity in relation to the bilaminar embryo and definitive yolk sac
above the bilaminar embryo disc and definitic yolk sac is underneath that
where is the chorionic cavity once implantation is complete
surrounding the entire embryo
where and when is the primitive streak formed
week 3, midline of caudal end of epiblast (amniotic cavity side)
what forms the cranial and caudal ends of the primitive streak
- cranial-primitive pit and node
- caudal-primitive groove
describe gastrulation
- epiblast cells move through the primitive streak forming 3 germ layers
- hypoblast cells are replacesd by endoderm
- cells migrating through the streak from the mesoderm
- epiblast cells become the ectoderm
- body axes established by primitive streak
what is the fate of the ectoderm
- skin
- nervous system
what is the fate of the overall mesoderm
divides into three layers either side of the notochord
what are the three layers of the mesoderm
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm (somatic)
- lateral plate mesoderm (visceral)
fate of paraxial mesoderm
- axial skeleton, skeletal muscle and parts of dermis (back)
fate of intermediate mesoderm
- urogenital systems and assoc. structures
fate of lateral plate mesoderm (somatic)
- most of dermis, lining of body wall, parts of limbs
fate of lateral plate mesoderm (visceral)
- CVS, mesothelial covering of organs, smooth muscle
fate of endoderm
- lining of gut tube, resp tract, bladder and urethra
