Early Embryogenesis Flashcards
What is embryogenesis?
Embryogenesis is the development of the zygote up to the end of eight week of intra-uterine life
Early embryogenesis begins with the formation of ………………, and ends when …………….. is formed
Early embryogenesis begins with the formation of zygote and ends when the primitive streak forms
Implantation is completed by the end of the ……… week of development
Implantation is completed by the end of the second week of development
Blastocyst, partially embedded in the endometrial stroma on day ……..
8
Trophoblast in the embryonic pole differentiates into cytotrophoblast and syncytio-trophoblast on day ……..
8
The inner cell mass or embryoblast differentiates into hypoblast layer (small cuboidal cells) and epiblast layer (high columnar cells) on the ……….day
8th
The two layers of the inner cell mass form a flat disc, hence the bilaminar germ disc on the ………. day
8th
The amniotic cavity develops within the epiblast on the ……… day
8th
The amnioblasts derived from the epiblast and epiblast form the wall of the amniotic cavity on day ………
8
Outline the developmental changes that occur on the 8th day of IUL
- Blastocyst, partially embedded in the endometrial stroma.
- Trophoblast in the embryonic pole differentiates into cytotrophoblast and syncytio-trophoblast.
- Inner cell mass or embryoblast differentiates into hypoblast layer (small cuboidal cells) and epiblast layer (high columnar cells).
- The two layers of the inner cell mass form a flat disc, hence the bilaminar germ disc
- Amniotic cavity develops within the epiblast.
- Amnioblasts derived from the epiblast and epiblast form the wall of the amniotic cavity.
the extraembryonic somatic mesoderm and the two trophoblast layers collectively form ……….
Chorionic plate
The ………….. later becomes the umbilical cord
connecting stalk
Growth of the bilaminar germ disc is relatively slow in comparison with the trophoblast, true or false
True
What is the size of the bilaminar germ disc during early embryogenesis?
The disc remains very small, 0.1 to 0.2mm, during the early embryogenesis
The blastocyst becomes more deeply embedded in the endometrium on day …….
9
…………… closes the defect at the implantation site.
Fibrin coagulum
Vacuoles appear in the syncytio-trophoblast layer at the embryonic pole on day ……
9
The vacuoles fuse to form large lacuna on day …….
9
How is the primitive yolk sac (excoelomic cavity) formed?
Primitive yolk sac (exocoelomic cavity) forms at the embryonic pole by flattened cells probably derived from the hyboblast
The flattened cells form a thin membrane called the Heuser’s membrane or exocoelomic membrane.
The membrane & the hyboblast form the wall of the primitive yolk sac.
The Heuser’s membrane and the hyboblast form ………..
the wall of the primitive yolk sac.
Outline the events that occur on the 9th day of IUL
Blastocyst , more deeply embedded in the endometrium .
Fibrin coagulum closes the defect at the implantation site.
Vacuoles appear in the syncytio-trophoblast layer at the embryonic pole.
The vacuoles fuse to form large lacuna – the lacunae stage of placental development
Primitive yolk sac (exocoelomic cavity) forms at the embryonic pole by flattened cells probably derived from the hyboblast
The flattened cells form a thin membrane called the Heuser’s membrane or exocoelomic membrane.
The membrane & the hyboblast form the wall of the primitive yolk sac.
Exocoelomic cysts refer to ………..
portions of the primitive yolk sac pinched off into the chorionic cavity.
What are the forms of abnormal blastocysts?
- Some consist of syncytium only
- Others show trophoblastic hypoplasia
- Abnormal orientation of the germ disc
- Absence of embryoblast (blighted ovum)
Mention the features of hyadatiform mole
- Little or no embryonic tissue
- Trophoblast develops and forms placental membrane
- Benign tumour may be produced by the mole
- Or malignant or invasive mole/choriocarcinoma may develop
Genetic analysis of the moles shows that ……………..
most moles arise from fertilization of an oocyte without a nucleus (duplication of the male chromosomes)
Microdeletion on chromosomes 15 leads to ………
- Prader - Willi syndrome - when inherited from the father
- Angelman’s Syndrome - when inherited from the mother.
The uteroplacental circulation is established on ……….
Beteween day 11-12
When does the blastocysts become completely embedded in the endometrial stroma?
Beteween day 11 and 12
Site of implatation, almost covered by the surface epithelium on …………
The period between day 11 and 12
The blastocyst slightly protrudes into the endometrial cavity on ……..
The period between day 11 and 12
How is a communication is established between the lacunae?
The syncytial lacunae become continuous with the congested and dilated maternal capillaries (maternal sinusoids).
Syncytio-trophoblast cells erode maternal sinusoids.
Then blood enters the lacunae system leading to establishment of utero-placental circulation.
The lacunae system is established on ……….
The period beteween day 11 and 12
Where is the extraembryonic mesoderm formed?
Extraembryonic mesoderm forms between the outer surface of the primitive yolk sac and the inner surface of the cytotrophoblast
When is the extraembryonic mesoderm formed?
Between day 11 and 12
……………….. forms when vacuoles that formed within the extra-embryonic mesoderm coalesce.
Chorionic cavity or extra-embryonic cavity
The chorionic cavity surrounds both the amniotic cavity and the primitive yolk sac except at a point called ……….
The connecting stalk
where is the bilaminar germ disc connected to the trophoblast layer?
At a point called the connecting stalk
Extraembryonic somatic mesoderm can be defined as?
the extraembryonic mesoderm covering the amnion
…………… is the extraembryonic mesoderm covering the yolk sac
Extraembryonic splanchnic mesoderm
The decidual reaction occurs on …….
The period between day 11 and 12
Describe the decidual reaction.
Endometrial cells become polyhedral, loaded with glycogen and lipids.
Extravasate fill the intercellular spaces.
The endometrium becomes oedematous.
The reaction spreads from the implantation site to the entire endometrium.
The site of implantation is usually healed by day …..
13
The trophoblast develops villous structures on day …….
13
Villi are ………
cellular columns of cyto-trophoblast covered by syncytio-trophoblast
What are excoelomic cysts?
portions of the primitive yolk sac pinched off into the chorionic cavity
