Second Week of Human Development Flashcards
When does implantation start and completed?
Implantation starts on day 6 and is completed by the second week.
What embyronic structures develop during the second week?
Amniotic cavity, amnion, umbilicle vesicle, connecting stalk, and the chorionic sac.
How does the cytotrophoblast help push the blastocyte into the endometrium?
It forms cells that increast the syncytiotrophoblast
What do the synctiotrophoblast cells do?
Secrete hcg and help pull the blastocyst into the endometrium by growing finger like projections into the connective tissue.
When is the placenta formed and how?
On day 11-12 the placenta is developed and takes over.
It forms after the lacunar network is developed and the syntiotrophoblasts erode the maternal capillaries allowing blood to seep in and out of the lacunar networks.
What cells provide nutrients?
Dicidual or endometrial cells provide nutrition by degenerating and engulfing cellular debris.
What two layers does the embryoblast seperate into?
- Epiblast layer
- Hypoblast layer
What is the purpose of the epiblast layer?
Gives rise to the three germ layers
- Ectoderm
- Mesoderm
- Endoderm
What is the purpose of the hypoblast cells?
Forms the roof of the yolk sac.
Later the cells are replaced with the endoderm.
Where do lacunae develop and what do they do?
In the outer layer cells (syntiotrophoblasts).
Lacunae become filled with a mixture of maternal blood from ruptured endometrial capillaries and cellular debris from eroded uterine glands.
How does maternal blood and cell debris get to the embryonic disc?
Via diffusion.
What is the embryonic disc?
The embryonic disc is the bilaminar plate of cells containing the epiblast and hypoblast cells.
Epiblast cells develop into the three germ layers
Hypblast cells forms the roof of the yolk sac/excolemic cavity
Which germ layer develops first?
The mesoderm
When does the mesoderm develop?
Day 12
How does the connecting stalk form and what does it do?
Day 12-13 the bilaminar disc (epiblast and hypoblast cells) joins the trophoblast cells by the extraembyryonic mesoderm, which becomes the connecting stalk.
This stalk will serve the primary pathway along where blood vessels of the embryo establish communication with the chorion and will later become the umbilical cord.
