Fertilisation to Trilaminar Flashcards
Where does fertilisation take place
ampulla
what does the sperm bind to in first stage of fertilisation
sperm binds in human specific interaction with zone pellucida glycoprotein (tough coat, fluid can enter)
during fertilisation what enzyme is released from sperm head and the enzymes function
acrosomal enzymes released, helps break down zone pellucida so sperm can digest its way into egg
sperm and egg membrane fuse and sperm contents enter egg
what sperm entry into egg trigger
completion of meiosis 2
release of cortical granules by oocyte
function of fimbriae
finger like projections responsible for moving oocyte from ovum to uterus
what are blastomeres
once fertilisation occurs the zygote - pronuclei (maternal and paternal) undergoes a series of mitotic divisions which subdivide the fertilised egg into smaller daughter cells
What cells are totipotent
up to 8 cell stage (16) blastomeres are thought to be totipotent
What is formed when there is 16 cells
morula
what is compaction
cell junction formation cells confined in zone pellucida maximise space by coming into closer contact with each other outer cells (in contact with zona pellucida) form extensive gap junctions
What are trophoblasts
embryonic part of placenta
form blastocyst wall
what is the name of the inner cell mass of an embryo
embryo proper/embryoblast/amnio and yolk sac
what has occurred 1 week after fertilisation
implantation in uterus
what happens once embryo reaches uterine cavity
blastocyst hatching, blastocyst breaks free of zone pellucida by breaking its walls so plantation occurs
what are the normal implantation sites
middle or upper dorsal uterine wall
what are the abnormal sites of implantation that can lead to ectopic pregnancy or miscarriage
ovary, ampulla, uterine tube, lower part of uterus, cervix, peritoneum
why is implantation of an embryo dangerous
wherever embryo implants a dense network of blood vessels form, if implantation in abnormal site vessels can rupture and haemorrhage
What is implantation driven by
trophoblasts
what do trophoblast divide into during implantation
cytotrophoblasts (made of individual cells)
Syncytiotrophoblasts (single multinucleated cells)
During implantation what 2 layers does the embryo organise into
epiblast - in dorsal surface of embryo
hypoblast in ventral surface of embryo
amniotic cavity begins to form
when is implantation complete
day 9
embryo - bilaminar disc
each layer associated with a different space: epiblast + amniotic cavity, hypoblast + yolk sac
from edges of the hypoblast cells move out and form original blastocyst membrane
what begins to form on day 12
chronic cavity begins to form within the extraembryonic mesoderm, trophoblastic lacunae fills with blood
what has formed on day 13
definitive/secondary yolk sac forms
What happens once the embryo is implanted and the placenta starts to form
syncytiotrophoblast extends and contacts maternal blood
where is the amniotic cavity located in the embryo
above the bilaminar embryonic disc and the definitive yolk sac below
