First and Second Week of Development Flashcards
What is an autoradiography? How is it conducted?
A way to identify the specific chromosomes.
The cell is cultivated in the presence of timidin, which is labeled by radioactivity.
When does compaction happen?
On day 3.
What is compaction?
Individual outer blastomere tightly adhere through E cadherins and gap junctions.
How do different cells develop?
The inside-outside hypothesis: depending on the position of the cells, this will determine its fate. If it’s in the outer position, then it will become the trophoblast. While if it’s in the core, it will become the inner cell mass.
The cell polarity model: different fates for cells depend on the plane that drives the type of differentiation.
What happens on day 4-5 of gestation?
Cavitation occurs, this is caused by the accumulation of Na+ (Na/K pump) and H2O among inner blastomeres.
Differentiation of the cells into the trophoblast and the inner cell mass also occurs.
When does the blastocyst attach to the lining epithelium of the endometrium?
On day 6.
When is a blastocyst formed?
A blastocyst is formed when cavitation has occured, at approximately day 5.
What is an ectopic pregnancy?
This is where the egg implants anywhere beside the normal area in the epithelial lining of the endometrium in the uterus.
Describe how the blastocyst cells differentiate.
The cells in the outer area will become the trophoblast, the envelope of the embryo. While the cells inside will give rise to the inner cell mass.
How does the blastocyst implant into the uterine wall?
When the embryo is implanting, there is a layer of surrounding trophoblast cells which mediate implantation.
They form protrusions (microvilli) and are initially single mononucleated, but start fusing together to form syncytiotrophoblast cells that mediate implantation.
These cells stimulate apoptosis of the maternal cells, which is important for the release of nutrients. The cells destroyed released molecules which are used by the syncytiotrophoblast cells to nourish the embryo.
What is the decidual reaction?
The endometrial connective tissue cells undergo a transformation, the decidual reaction.
After the cells swell because of the accumulation of glycogen and lipid in their cytoplasm, they are known as decidual cells.
This enlargement of the cell is important for its nourishment, as there is no endogenous system at the moment to guarantee oxygen and nutrients.
What is cavitation? How does it happen?
Cavitation is when a cavity is formed inside the morula.
Accumulation of Na+ (Na/K pump) and H2O among inner blastomeres causes ‘cavitation’.
What do trophoblasts differentiate into when in contact with the endometrium?
Into syncytiotrophoblasts and cytotrophoblasts.
What does the inner cell mass differentiate into?
Into hypoblasts and epiblasts.
How is the excocoelomic membrane (Heusser’s) formed?
When the hypoblast cells proliferate and covers the blasto cell cavity, also transforming into a primitive yolk sac.
How is the extraembryonic mesoderm formed?
The cells of the Heuser’s membrane and the cytotrophoblast cells that surround it release an extracellular matrix
When does the extraembryonic mesoderm first appear?
Approx at 10 days.
What is the chorionic cavity? How does it form?
The chorionic cavity is formed from lacunae in the extraembryonic mesoderm that fuses together.
It will surround the entire embryo.
Approximately when does the chorionic cavity form?
Approximately 12 days.
What happens after the chorionic cavity forms?
The formation of the chorionic cavity will delaminate the extraembryonic mesoderm forming 2 layers - an external layer called the somatic extraembryonic mesoderm and a layer surrounding the embryo.
This layer will undergo constrictions that will detach parts of the yolk sac. This forms a smaller yolk sac called the definitive (secondary) yolk sac.
Describe the changes that the trophoblastic lacunae undergoes.
By approximately day 12, the lacunae stop growing and fuse to form lacunar networks.
Capilaries in the endometrium surrounding the developing embryo dilates, forming maternal sinusoids.
As syncytiotrohoblasts expand, enzymes
Name and describe the structures formed at the 2nd week of development.
Epiblast forms the embryo.
Yolk sac will be the first hematopoietic site.
Amnion will contain the liquid where the embryo will grow.
Chorion will form the placenta.
Body stalk forms the umbilical cord.
Describe the structure of the amniotic sac and its surroundings at the end of 2nd week.
The embryo is joined to the trohphoblast by a band of extraembryonic mesoderm called the connecting stalk.
The amniotic cavity is lines by amneoblasts (from epiblasts). Then a layer of epiblasts on top of hypoblasts.
The paternal and maternal genome contributions are not equivalent, how is this proven?
An experiment involving changing the pronucleus from the egg or sperm under different conditions.
The control results in an normal embryo and placenta.
An egg or sperm derived from another zygote results in a normal embryo and placenta.
2 sperm derived or egg derived zygote: In the sperm condition, results in stunted embryo and nearly normal placenta.
In egg condition, results in nearly normal embryo, small placenta.
