Lecture 11 - Pre-implantation Development Flashcards
The oocyte is surrounded by a layer called the ______
Zona pellucida
Describe the stages between oocyte to blastocyst (5)
Oocyte + sperm
Single cell zygote
2 cell embryo
Morula
Blastocyst
What does the zygote become after multiple cell divisions?
Multicellular embryo
In the early embryo, cell numbers ____ while mass _____ this is possible as daughter cells become _____
In the early embryo, cell numbers increase while mass stays constant. This is possible as daughter cells become increasingly smaller.
What are blastomeres?
Cells formed by cleavage
What is compaction?
When cells become tightly packed past the 8-cell stage
What is the morula?
Solid ball of 16 blastomeres, surrounded by zona pellucida
What is the difference between the inner cell mass and the trophoblast?
The inner cell mass consists of cells on the inside of the morula
The trophoblast consists of cells on the outside of the morula (syncytial or cellular)
What is YAP and what does it do?
YAP
List the 3 models explaining differentiation of embryonic cells into ICM and trophoblast
- Mosaic model - no longer accepted
- Positional model - differentiation depending on if completely surrounded or not / exposure to external environment
- Polarity model - parallel = both polar and outside, orthogonal = one polar (trophoblast) and the other apolar (ICM)
Describe the process of cavitation
Fluid moves through the trophoblast into the centre of the morula and forms a cavity - blastocyst cavity/blastocoele - organism now known as a blastocyst
What happens to the ICM when the blastocoele expands?
The ICM is pushed to one end of the fluid filled ball
What is the breakdown of the zona pellucida referred to?
Hatching
How does the bilaminar embryo arise? What happens at this stage?
ICM becomes divided into two different layers: hypoblast and epiblast
Embryo implants at this stage
What does the epiblast become?
All tissues forming part of the human fetus
What does the hypoblast together with the epiblast contribute to?
Extra-embryonic support structures
Describe the formation of the amniotic cavity
Roof formed by squamous cells which create a membrane known as the amnion - derived from the epiblast
Floor of amniotic cavity formed by epiblast proper
Amniotic cavity filled with amniotic fluid
Describe the formation of the yolk sac and its function
Cells derived from the hypoblast begin to migrate and eventually cover the inside surface of the blastocoele, forming a new cavity known as the yolk sac.
Provides blood cells to the embryo and gives rise to the germ line that will migrate into the gonads. Relatively empty in humans and nourishes embryo during 2/3 week of development.
