| How and what is the puprose of modifiying the glycoprotein coat of sperm cells | It is modified by factors released by the epithelium of the uterine tube
Function is to allow the sperm to penetrate the oocyte |
| How long is the pre-embryonic period and embraynoic period | Pre --> 1-2 weeks after fertilisation
Embryanic period --> 3-9 weeks after fertilisation |
| What are the hormones used in contraception | Oestrogen and Progresterone inhibit ovulation and change the uterine lining which inhibits the passage of the sperm and makes implantation unlikely |
| When does cleavage begin | Begins 30 hours after fertilisation and produces two blastomeres of equal size |
| What happens at the 16 cell stage - Morula | The initial loose grouping becomes more compact by the process of compaction
Cells are held together via tight junctions and communicate via gap junctions |
| What is the outer cell mass called? | Trophoblast
However, this remains enveloped by the zona pellucida |
| Inner cell mass name and what does it do | Embrayoblast and forms all tissues of the embrayo |
| When and Why is hatching needed | Around day 4 and is due to the building pressure of increasing number of cells
This hatching from the zona pellucida allows the blastocyst to enlarge and implant |
| By the end of Week 1 what do you have? | Blastocyst contains around 100 cells
Trophoblasts begins to interact with the uterine epithelium
Embrayoblasts are going to start giving rise to the embrayo
Remaining cells will form the fetal membranes |
| Week 2 , what does the trophoblast differentiate into? | 2 cell layers
- Cytotrophoblast --> contains trophoblast stem cells
- Synchcytiotrophoblast --> Invasive layer of cells originating from the cytotrophoblast |
| In Week 2 , what does the inner cell mass differentiate into | Epiblast --> forms all embrayonic tissues
Hypoblast
These structures forms the bilaminar disc |
| When can chorionic villus sampling be taken? | Early as 8th week but more commonly taken at the 11th and 24th weeks |
| Where is the human choronic gonadotrophin secreted from and function | hCG is secreted from the syncytiotrophoblast cells and is important in stimulating the uterus to support the developing conceptus |
| Overview of gastrulation | Takes place in the third week
The bilaminar disc is converted to trilaminar consisting of the three germ layers ( ectoderm, mesoderm and endoderm )
The notochord forms along the longitudinal axis |
| In the Week of 3, what is formed | 3 cavities --> Amniotic cavity, Definitive yolk sac and Chorionic cavity
3 germ layers --> Endoderm, Ectoderm and Mesoderm |
| How are the 3 germ layers formed? | Hypoblast is displaced by endoderm by migrating epiblast cells |
| What is the role of the notochord | Notochord defines the midline and the axial skeleton forms around it e.g. rib cage and skull
It induces the ectoderm to thicken forming a neural plate from which the neural tube forms |
| Fates of the three germ layers ? | Ectoderm : Forms organs and structures that maintain contact with the outside world such as the nervous system and epidermis
Mesoderm forms supporting tissues such as muscle and cartilage
Endoderm forms internal structures such as epithelial linings of tracts |
| What is teratogenesis | Process of which normal embryonic development is disrupted since Week 3-8 is most sensitive
E.g. thalidomide and other infectious agents |
| How is the notochord formed | A subset of the epiblast cells migrating through the primitive pit towards the cranial pole form a notochondral plate continuous with the endoderm
THese cells proliferate and detach from the endoderm to form a solid rod of cells running in the midline |
