Embryology Lecture 2-Week 2 and 3 Development of Bilaminar and Trilaminar Disc Flashcards
By ______ post-fertilization - implantation into the endometrial wall is completed.
By 10 days post-fertilization - implantation into the endometrial wall is completed.
The trophoblast differentiate into:
The trophoblast differentiate into:
- ) Cytotrophoblasts
- Dervied from Trophoblasts
- Mitotic mononuclear cells
- Migrate to become Syncytiotrophoblasts - ) Syncytiotrophoblasts- -Multinuclear cells without cell membranes
- Responsible for erosion into the endometrium
- Produce the HCG preserving corpus luteum activity (secretion of E and P4)
Describe the establishment of embryonic and bilaminar structure:
After fertilization occurs:
- A small space is created within the embryoblast
- Amnioblasts surround this space enclosing the cavity
- This space will go on to become the amniotic cavity
- The embryoblast forms a flat bilayer structure, embryonic disc, consisting of two layers:
- ) Epiblast-Columnar cells
- ) Hypoblast-Small cuboidal cells
Describe the establishment of maternal blood communication:
- By Embryonic Day 11-12 the blastocyst will completely embed in the endometrium and the surface defect will close and heal
- Synctiotrophoblasts will penetrate deeper into the maternal capillaries termed sinusoids.
- This establishes uteroplacental circulation
Describe some support structures to the embedded blastocyst:
- Exocoelomic membrane- Lines inner surface of cytotrophoblasts
- Along with hypoblasts this forms the lining of the primitive yolk sac (also termed the exocoelomic cavity)
What is the function of the yolk sac?
to provide nourishment for the developing embryo
Describe the formation of the Extraembryonic Mesoderm:
- Cells intervene between the cytotrophoblast layer and the yolk cavity forming the extraembryonic mesoderm.
- This layer fills all space between the trophoblasts and the amnion and exocoelomic cavity.
- Within this mesoderm a space termed the extraembryonic cavity or chorionic cavity is formed surrounding the yolk sac and amniotic cavity.
It is within the _______ cavity that villi will develop to allow for uteroplacental circulation.
It is within the chorionic cavity that villi will develop to allow for uteroplacental circulation.
The extraembryonic mesoderm layer further differentiates into:
The extraembryonic mesoderm layer further differentiates into:
- Somatic layer- lines and supports/surrounds the cytotrophoblast and amnion
- Sphlanchnic layer - lines and supports/surrounds the yolk sac
_________ form the primary villi establishing communication with the chorionic cavity.
Trophoblasts form the primary villi establishing communication with the chorionic cavity
The hyoblast layer produces cells that migrate along the exocoelomic membrane and form a new cavity termed the _________. These migrating cells pinch off the yolk sac from the __________.
The hyoblast layer produces cells that migrate along the exocoelomic membrane and form a new cavity termed the secondary or definitive yolk sac. These migrating cells pinch off the yolk sac from the endometrium.
At the end of week 2:
- Chorionic cavity continues to expand.
- The somatic layer of mesoderm is now properly termed _______ _______.
- The connecting stock is now visible traversing the extraembryonic mesoderm.
- This connecting stock will go on to become the _______ _____.
At the end of week 2:
- Chorionic cavity continues to expand.
- The somatic layer of mesoderm is now properly termed chorionic plate.
- The connecting stock is now visible traversing the extraembryonic mesoderm.
- This connecting stock will go on to become the umbilical cord.
Early week 3 development is characterized by 6 things:
- Appearance of Primitive Streak
- Development of the Notochord
- Transition from two layer embryo to three layer embryo (gastrula)
- Establishment of body axes
- Further growth of the embryo
- Further development of uteroplacental circulation
Describe the formation of the primitive streak:
- Forms in the surface of the upper layer, the epiblast during week 3
- Establishes the body axis
- Becomes the site of gastrulation.