2nd week of development Flashcards
3 events take place during the 2nd week of development
I. Completion of implantation of the blastocyst
II. Formation of bilaminar embryonic disc(epiblast and hypoblast)
II. Formation of extraembryonic structures(amniotic cavity, amnion, umbilical vesicle [yolk sac], connecting stalk, and chorionic sac)
DAY 8
At the eighth day of development, the blastocyst is partially embedded in the ___
endometrial stroma
DAY 8
At the eighth day of development, the ___ is partially embedded in the endometrial stroma
blastocyst
DAY 8
In the area over the embryoblast, the trophoblast has differentiated into two layers.
What are they?
(1) an inner layer of mononucleated cells, the cytotrophoblast
(2) an outer multinucleated zone without distinct cell boundaries, the syncytiotrophoblast
DAY 8
Mitotic figures are found in the ___
cytotrophoblast
DAY 8
cells in the cytotrophoblast divide and migrate into the ___, where they fuse and lose their individual cell membranes.
cytotrophoblast
DAY 8
Cells of the inner cell mass or embryoblast also differentiate into two layers
→ What are these 2 layers
(1) hypoblast layer - a layer of small cuboidal cells adjacent to the blastocyst cavity
(2) the epiblast layer - a layer of high columnar cells adjacent to the amniotic cavity,
DAY 8
The hypoblast and epiblast layers together form a flat ovoid shaped disc called the __
bilaminar embryonic disc
DAY 8
Cells of the inner cell mass or embryoblast also differentiate into two layers which are hypoblast and epiblast layers → the layers form a flat disc
→ a small cavity appears within the ___
epiblast
DAY 8
a small cavity appears within the epi- blast. This cavity enlarges to become the __
amniotic cavity.
DAY 8
What are amnioblasts?
Epiblast cells adjacent to the cytotrophoblast
→ ogether with the rest of the epiblast, line the amniotic cavity
DAY 9
The blastocyst is more deeply embedded in the endometrium, and the ___ in the surface epithelium is closed by a fibrin coagulum
penetration defect
DAY 9
The blastocyst is more deeply embedded in the endometrium
→ the penetration defect in the surface epithelium is closed by a ___
fibrin coagulum
DAY 9
Describe the lacunar stage
The phase of trophoblast development
→ Vacuoles appear at the region of the trophoblast and they fuse to form lager lacunae
What is exocoelomic (Heuser’s) membrane? What does it form?
A thin membrane formed by the cells of the hypoblast adjacent to the cytotrophoblast
→ lines the inner surface of the cytotrophoblast
→ forms the lining of the exocoelomic cavity, or primitive yolk sac or primary umbilical vesicle
When is the blastocyst completely embedded in the endometrium?
11th - 12th day of development
11th - 12th day of development
What happen before primordial uteroplacental circulation?
cells of the syncytiotrophoblast penetrate deeper into the stroma(tissue)
→ erode the maternal sinusoids (the endothelial lining of the maternal capillaries.)
→ The syncytial lacunae become continuous with the sinusoids
→ maternal blood enters the lacunar system
→ maternal blood begins to flow through the trophoblastic system
→ primordial uteroplacental circulation begins
11th - 12th day of development
What is extraembryonic mesoderm? Its role?
cells which are derived from yolk sac cells form a fine, loose connective tissue
→ fills all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally
11th - 12th day of development
What is chorionic cavity?
Cavity developed in the extraembryonic mesoderm
11th - 12th day of development
What is extraembryonic somatic mesoderm?
The extraembryonic mesoderm lining the cytotrophoblast and amnion
11th - 12th day of development
What is extraembryonic splanchnic mesoderm?
the lining covering the yolk sac
11th - 12th day of development
What is decidual reaction?
the endometrial connective tissue cells undergo a transformation
→ the decidual cells of the endometrium swell because of the accumulation of glycogen and lipid in their cytoplasm
11th - 12th day of development
The primary function of the decidual reaction is __
to provide nutrition for the early embryo and an immunologically privileged site for the conceptus
What happen to surface epithelium and blood flow in day 13th?
The surface defect in the endometrium has been completely covered by the surface epithelium
Occasionally bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces
DAY 13
The trophoblast is characterized by __
The surface defect in the endometrium has been completely covered by the surface epithelium
Occasionally bleeding occurs at the implantation site as a result of increased blood flow into the lacunar spaces
DAY 13
The role of Cells of the cytotrophoblast
They proliferate locally and penetrate into the syncytiotrophoblast, forming cellular columns surrounded by syncytium.
DAY 13
Cellular columns with the syncytial covering are known as ___
They proliferate locally and penetrate into the syncytiotrophoblast, forming cellular columns surrounded by syncytium.
DAY 13
How is secondary yolk sac formed?
the hypoblast produces additional cells that migrate along the inside of the exocoelomic membrane
→ cells proliferate and gradually form a new cavity within the exocoelomic cavity → known as the secondary yolk sac or definitive yolk sac
DAY 13
This secondary yolk sac is much ___ than the original exocoelomic cavity, or primitive yolk sac.
smaller
DAY 13
Meanwhile, the extraembryonic coelom expands and forms a large cavity, the __
chorionic cavity
DAY 13
The extraembryonic mesoderm lining the inside of the cytotrophoblast is then known as the ___
chorionic cavity
DAY 13
The ___ lining the inside of the cytotrophoblast is then known as the chorionic plate.
extraembryonic mesoderm
DAY 13
The only place where extraembryonic mesoderm traverses the chorionic cavity is in the ___ With development of blood vessels, the stalk becomes the___
connecting stalk
umbilical cord.
- The second week of development is known as the week of 2’s. Formation of what structures supports this statement?
- The trophoblast differentiates into two layers: the cytotrophoblast and syncytiotrophoblast.
- The embryoblast forms two layers: the epiblast and hypoblast.
- The extraembryonic mesoderm splits into two layers: the somatic and splanchnic layers.
- Two cavities form: the amniotic and yolk sac cavities.
