Embryology Flashcards
Embryology
Study of embryonic development
Teratology
Study of abnormal embryonic development
Defines the lateral sides of a body
Sagittal plane
Defines the anterior and posterior sides of a body
Coronal plane
Defines the superior and inferior sides of a body
Transverse plane
Fertilization
Spermatozoan and oocyte unite to form the zygote (~24hrs)
Fertilization marks the start of …
the pre-embryonic period
Metabolic activation after fertilization initiates…
cleavage of the zygote (cell division)
Cleavage: Each cell is called a … and is surrounded by the ….
Each cell is called a blastomere and is surrounded by the zona pellucida.
Why does the zygote size remain the same during the initial stages of cleavage?
Because the blastomeres are surrounded by a membrane called the zona pellucida which constrains the growth of the zygote, leading to compaction
Describe what happens at the 8-cell stage of the zygote
Compaction: cells are tightly aligned, allowing for better cell interaction
Describe what happens at the 12-32-cell stage of the zygote
This stage is referred to as the morula stage because the blastomeres are so compacted. It is at this stage that the zygote enters the uterus.
Once the zygote enters the uterus (~day 5), it is referred to as the … because…
Once the zygote enters the uterus, it is called a “blastocyst” because the morula is hollowed out and the blastocystic cavity (fluid-filled) begins to form
The blastocystic cavity separates the blastocyst into 2 layers (inner and outer) called
trophoblast (outer layer - future placenta) and embryoblast (inner layer - future embryo)
The trophoblast secretes the …
Early Pregnancy Factor, which forms the basis of a pregnancy test during the first 10 days. EPF has immunosuppressant properties.
- Fertilization
- Cleavage
- ?
- Implantation
First step of implantation
Blastocyst binds the endometrial lining (epithelium) of the uterus
Upon implantation, the trophoblast differentiates into two layers…
- syncyntiotrophoblast (invades endometrial epithelium)
- cytotrophoblast (adjacent to the embryoblast)
Why does the syncyntiotrophoblast invade the endometrial epithelium?
To establish nutrient circulation (nourishment for the future embryo is derived from eroded maternal tissue).
Day 8: Blastocyst starts to become embedded in the endometrium.
Day 9: ?
Day 9: Lacunae (small cavities) start to develop in the syncytiotrophoblast
What is the role of lacunae?
They eventually become filled with maternal blood and establish the uteroplacental circulation (serve as a direct connection to maternal blood)
After the blastocyst sinks beneath the endometrial lining, the implantation site is filled by…
a closing plug (fibrin coagulum)
If closing plug does not form at the site of implantation, what can happen?
Abnormal bleeding
Fusion of the lacunae leads to the formation of…
the lacunar network
Once the lacunar network is established, the syncyntiotrophoblast begins to…
erode the endometrial capillaries in order to establish the uteroplacental circulation
After implantation , the embryoblast differentiates into the…
bilaminar disk (2 layers)
What are the two layers of the bilaminar disk?
Hypoblast (primary endoderm)
Epiblast (primary ectoderm)
Thick layer of columnar cells related to the amniotic cavity
Epiblast
Layer of cuboidal cells facing the blastocystic cavity
Hypoblast
Describe the formation of the amniotic cavity
A later of the epiblast becomes the amnioblast and separates from the epiblast to form the amnion enclosing the amniotic cavity.
Hypoblast migrates to populate the inner surface of the blastocystic cavity, forming the …
exocoelomic membrane surrounding the exocoelomic cavity
Hypoblast + exocoelomic membrane form the …
primary umbilical vesicle (yolk sac)
Epiblast forms the
amnion
Hypoblast forms the
yolk sac
The amniotic cavity and the exocoelomic cavity are separated by the…
embryonic disk
Layer of connective tissue formed between the exocoelomic membrane and cytotrophoblast
Extraembryonic mesoderm
Function of extraembryonic mesoderm
- Surrounds the amnion and primary umbilical vesicle
- Separates embryoblast from trophoblast
Around day 12-13, cavities form in the extra embryonic mesoderm. These cavities begin to merge to form the…
extraembryonic coelom (cavity)
The extraembryonic coelom separates the extraembryonic mesoderm into:
- Extraembryonic somatic mesoderm (lines the trophoblast - future body wall)
- Extraembryonic splanchic mesoderm (lines the yolk sac - future viscera)
The extraembryonic mesoderm surrounds the amnion and secondary umbilical vesicle everywhere except at the…
connecting stalk
The late 2nd week of pre-embryonic development marks the…
1st stage of the placenta
Placenta
Fetomaternal organ for metabolic exchange between the mother and embryo
The extraembryonic mesoderm induces the 2 layers of the trophoblast to grow into the endometrium, forming…
primary chorionic villi
Function of primary chorionic villi
Primary chorionic villi maximize the surface-area in contact with maternal blood for nutrient and gas exchange