Embryology Flashcards
What is/describe gastrulation.
The process that converts a bilaminar disc to a trilaminar disc, the three layers being ectoderm, mesoderm, endoderm.
How many layers are present after gastrulation?
Name them from top to bottom
Three
Ectoderm
Mesoderm
Endoderm
How many layers are present prior to gastrulation?
Name them in order of top to bottom
Two
Epiblast
Hypoblast
What process leads to the formation of three layers from two?
Describe what happens.
Invagination
Epiblast cells migrate to the primitive streak
They differentiate and divide and push through the epiblast layer
Come to form mesoderm (invagination)
Where does implantation occur in placenta previa?
Posterior uterine wall
What has the notochord developed from? (Which layer)
Mesoderm
In what direction does development happen?
Cephalocaudally
What ensures particular organs develop on a certain side?
The primitive node has ciliated cells which waft signalling molecules in a certain direction causing a cascade which leads to development on a certain side
What is it called when organs develop on the opposite side?
Complete mirror imaging viscera
What is complete mirror imaging viscera? When may it cause problems?
When the organs (viscera) have developed and so are present on the opposite side
Problem when mirror-imaging is incomplete (IE a mix of normal and mirror image)
What features aid the movement of a zygote?
Fimbriae- sweep it along
Cilia- waft along
Muscular contractions of Fallopian tubes
What surrounds the oocyte? What is its role?
Zona pellucida Glycoprotein shell Prevents polyspermy Restricts size of cells from first few mitotic divisions Aids binding of sperm
Which cells in an early embryo are totipotent?
Morulla (16 cell stage)
Cells that are totipotent can…..
Develop or differentiate into anything
At what pre-embryonic stage is a fertilised oocyte from IVF transferred into the uterus?
Morulla stage
Which cells are pluripotent?
Blastocyst cells
Before compaction it is called a morula, what is it called afterwards?
Blastocyst
What process leads to the formation of a 16-cell morula?
Cleavage (mitotic divisions of the cells)
What marks the onset of gastrulation?
The formation of the primitive streak
What happens during compaction?
Fluid penetrates zona pellucida
Forms blastocoele cavity
Cells form tight junctions and form two masses- inner (embryoblast), outer (trophoblast)
This is now a blastocyst
On which day does hatching occur? What is it and what does it facilitate?
Day 5
The blastocyst ‘hatches’ out of the zona pellucida
It is now free to enlarge and interact with endometrium
After further differentiation, what layers do the embryoblast and trophoblast form? What is the name of one structure?
Inner (embryoblast)–> epiblast + hypoblast= bilaminar disc
Outer (trophoblas)–> syncitiotrophoblast + cytotrophoblast
During the formation of the bilaminar disc, what cavity forms?
Primitive yolk sac
What suspends the yolk sac? What will it later become?
Connecting stalk
Later becomes umbilical cord
