Flashcards in Embryology : Early human development Deck (43)
Describe the phases of fertilisation.
1. Penetration of the corona radiata
2. Penetration of the zona pellucida
3. Fusion oocyte and sperm cell membrane + Secondary oocyte in 2nd meiotic division
Name and describe features of the sperm molecule.
-Acrosome- sack which carries enzymes to allow fertilisation to take place
Midpeice – engine of sperm
Flagellum- beats for movement of sperm
Does corona radiata and zona pellucida provide a barrier to sperm?
Corona radiata- does not provide barrier for sperm
Zona pellucida- does provide a barrier
what is a zygote?
single cell embryo
what does sperm entry trigger?
Sperm entry triggers cortical granule release in egg cortex triggering formation of fertilisation membrane, which is impenetrable to sperm
what does fusion of the male and female pronuclei restore?
restores the diploid number of chromosomes = zygote, day 0 of development
How long does the zona pellucida remain during development?
first few days
what is cleavage?
Period of rapid cell division (no size increase)
is there an increase in cell size during cleavage?
No because the cell size is limited by zona pellucida
what happens to the morula under pressure?
changes into the blastocyst
Describe the structure of the blastocyst.
-outer wall- trophoblast
-inner cell mass- embyoblast
Describe the blastocyst hatching.
-Inner Cell Mass gives rise to the embryo, remaining cells form the trophoblast which contributes to the placenta
-Embryonic Stem (ES) cells are derived from the ICM
- Following hatching from the zona pellucida the embryo now interacts directly with the endometrial lining of the uterus
where does the blastocyst normally implant?
dorsal wall of uterus
where are abnormal implantation sites?
3. uterine tube
5. internal os of uterus
what is the maternal response after implantation?
new blood vessels form -maternal response
What happens during implantation?
-blastocyst makes contact with uterine epithelium
-Trophoblast sends projections into epithelium – breakdown connecting cells and crawl in
- trophoblast is now differentiated
-leading edge - syncytiotrophoblast
-Cytotrophoblast –remaining part of trophoblast
what ways does the cell face ?
-Emybroblast – 2 cells: one facing into cavity of blastocyst and one adjacent to trophoblast (epiblast)
- epiblast are proliferating – producing early cells of amnioablast
what happens to the implanted embryo at 9-12 days.
-The syncytiotrophoblast has extended and by erosion contacts maternal blood supply.
- The amniotic cavity is present above the bilayered embryonic disc and the definitive yolk sac below
-The chorionic cavity has developed and encircles the entire embryo
what is gastrulation?
formation of the germ layers
what are the 3 germ layers?
-Ectoderm : nervous system and skin
-Mesoderm: Muscle, bone and internal organs
where do cells migrate through?
Describe the process of gastrulation.
-Surface of epiblast is not uniform surface – impression at one end –buccopharyngeal membrane (cranial end) and primitve streak at one end – -drives prosess of gastrulation for 3 germ layers
Primitive streak sends signal – some epiblasts will come towards primitive streak and go deep into it and some go into hypoblast and some fill space (3 germ layers)
what is neurulation?
formation of the neural tube
what is the first step of neurulation?
An area of the ectoderm is induced to form Neural Tissue
when does neurulation start?
once gastrulation finishes
how is the brain formed during neurulation
In response to signals from mesoderm, some ectodermal cells differentiate and become neural
Then neural plate expands –produces brain - the different areas of brain i.e dicephalon
what happens at day 19/20 of neurulation?
-Creates hinge point along midline-pulling edges of neural tube upwards – pulls ectoderm with them as they are connnected
-The groove gets deeper over time
-Midpoint of embyro- make contact with one another – the neural edges fuse with one another and pulling ectoderm with them so will fuse with each other over the top and so neural tube is hidden
-Fiusion contines in both direction to enclose the entire neural tube
what happens during neural tube formation at day 23?
Anterior part close first
Undergo Epithelial to Mesenchymal transition and leave the neuroectoderm to enter the mesoderm