Early Embryonic Development 1 Flashcards
Where is the ideal site for implantation?
Posterior uterine wall
Where is the oocyte fertilised by the sperm?
In the AMPULLA of the Fallopian tube
What is a zygote?
Fertilised oocyte
What is the role of the zona pellucida?
- GLYCOPROTEIN SHELL
- Prevents the blastomeres from expanding
When does the first mitotic division of the zygote take place?
30hrs after fertilisation
Define ‘totipotent’
Undifferentiated cell that has the capacity to become ANY CELL TYPE
How is the morula formed?
Cleavage of the zygote within the zona pellucida into many undifferentiated cells
What are the products of compaction?
- Inner cell mass - EMBRYOBLAST
- Outer cell mass - TROPHOBLAST
Why are the cells pluripotent after compaction?
- Have the capacity to become MANY cell types but cannot be ANY cell type
- Embryoblast cells go on to form the embryo
- Trophoblast cells go on to form the supporting cavity and do not contribute to the body
What is the process of hatching?
- Blastocyst hatches from the zona pellucida
- Blastocyst can now interact with the posterior uterine wall and implant
How many cells does the conceptus consist of before implantation?
107
How many cells from the conceptus become the embryo?
~8
What does the trophoblast differentiate into during week 2?
- SYNCYTIOTROPHOBLAST
- CYTOTROPHOBLAST
When does the bilaminar disk form?
Week 2
Describe the formation of the bilaminar disk
- Differentiation of the inner cell mass (embryoblast) into 2 LAYERS
- EPIBLAST and HYPOBLAST
Where does the amniotic cavity lie?
Between the outer cell mass and the epiblast
Describe how implantation occurs
- INTERSTITIAL
- Uterine epithelium is breached and conceptus implants within the uterine storms
Explain the role of implantation
- ESTABLISHES MATERNAL BLOOD FLOW WITHIN THE PLACENTA
- Support of embryo changes from histotrophic to haemotrophic
What is the difference between histotrophic and haemotrophic?
- HISTOTROPHIC is when the embryo absorbs nutrients through the tissues by diffusion
- HAEMOTROPHIC is when the embryo obtains nutrients from the maternal blood
What is meant by an ECTOPIC PREGNANCY?
- Implantation occurs at a site other than the uterine body
- Can be PERITONEAL or OVARIAN (Fallopian tube)
- LIFE-THREATENING
Explain why an ectopic pregnancy may be life threatening for the mother
Implantation in an inappropriate site may cause HAEMORRHAGE
What is meant by PLACENTA PRAEVIA?
- Implantation occurs at the LOWER UTERINE SEGMENT
- May cause haemorrhage
- Requires a C section
Which implantation defect may require a C section?
Placenta praevia
Describe the formation of the primitive yolk sac
- Formed at the ABEMBRYONIC POLE
- Yolk sac membrane is in contact with the cytotrophoblast
