Early Embryonic Development Flashcards
What are the steps in development of a human being?
\+ Fertilisation \+ Single cell \+ Ball of cells \+ Cavities and two layered disc \+ Three layered disc with middle layer \+ Segments in middle layer \+ Tube forms from two outer layers (nervous system and gut) \+ Fully formed body form/organs
Where does fertilisation occur?
In the ampulla of the uterine tube within 12 hours of ovulation.
What kind of cells are sperm and ovum?
Haploid (23)
What is restored by fertilisation?
The diploid number of chromosomes (46)
What is cleavage?
+ First stage of embryogenesis
+ Repeated mitotic division of a zygote into blastomeres that cluster to a compact mass called morula.
+ Continues until blastula is formed.
When does initiation of cleavage occur?
Within 36 hours of fertilisation
What is a feature of cells up until the blastocyst stage?
They are totipotent
What is a blastula?
A blastula in which some differentiation of cells has occured
When does ovulation to implantation occur?
The first week of development
When does compaction begin?
At 8 cells ( central cells linked by gap junctions)
What is a morula?
A solid ball of cells with inner and outer layers (16+ cells)
What happens to the morula approx. 3-4 days after fertilisation?
+ Transported along the uterine tube and arrives at the uterus (~30-40 cells)
+ Zona pellucida disappears
+ Outer cells divide to become trophectoderm, inner cells become inner cell mass
What happens after 4.5 days?
+ Cavities form in the inner cell mass
+ Blastocyte is formed from trophoblast and inner cell mass
+ Still free unattached in uterus
When are cells totipotent up until?
The blastocyte stage
During what stage is it preferred that cells be sampled at for genetic testing?
+ Trophectoderm (5-6 days) now preferred over blastomere sampling
+ Previously inner cell mass sampling was used over this method
+ Searching for gene disorders or chromosome abnormalities
