Gastrulation Flashcards
When is the embryonic period?
Weeks 3-8 inclusive
Why is the embryonic period significant?
- It’s the period of greatest change
- Most perilous
What happens during the embryonic period?
All major and structures and systems are formed
What are germ layers?
Rudimentary lineages from which all others will arise
What does the bilaminar disc consist of?
NAME?
What happens to the epiblast in the embryonic period?
It undergoes radical development process
What is the result of the radical development of the epiblast?
3 germ layers established
What is gastrulation?
The process establishing the trilaminar disc, which consists of the 3 germ layers, and hence origin of all tissues of the body
What are the set axis observed in adults?
- Anterior / posterior
- Dorsal / ventral
- Right / left
What marks the onset of gastrulation?
The appearance of the primitive streak
What is the primitive streak?
The process thats driving and coordinating the gastrulation process
What is associated with the primitive streak?
The primitive node and the primitive pit
Where does the primitive streak have major significance?
In terms of the legal ramifications of the study of embryos
What happens once the primitive streak has formed?
Cellular rearrangement
Where does cellular rearrangement occur?
Within the epiblast of the bilaminar disc
In what ways to the cells rearrange?
NAME?
Is migration controlled?
Yes, highly
How far to cells migrate?
Widely
What happens in invagination?
The cels interdigitate themselves within other layers
What does the epiblast look like at the end of the second week?
Featureless, all cells look exactly the same
When does the primitive streak appear?
~day 16
Where does the primitive streak appear?
The dorsal surface of the epiblast
Describe the primitive streak
NAME?
Where does the primitive streak occur on the disk?
At one edge, but can be anywhere along the edge
Where is the primitive node located?
At the cranial end of the stalk
What is the cranial end of the stalk?
The end furtherest away from the outside of the epiblast
Where is the function of the primitive node?
It’s the co-odinating centre, co-ordinating and regulating all of the cells signals, and responsible for causing migration
Where is the primitive pit located?
At the centre of the node
What happens as gastrulation proceeds?
We see rapid morphological changes
What morphological changes do we see during gastrulation?
The establishment of 3 germ layers
What happens to the primitive streak once the 3 germ layers are established?
It regresses
What is the clinical significance of the regression of the primitive streak?
Occasionally it doesn’t regress, which has consequences
In what direction does development proceed?
Cranial → caudal
What is the result of the direction of development?
The head is always more developed than the feet, until fully grown
What happens to the epiblast of the bilaminar disc in gastrulation?
The cells migrate
What happens as the cells of the epiblast migrate?
They divide and differentiate as they do
What is the result of the migration of the cells of the epiblast?
Forms a new layer
How does the migration of the cells of the epiblast cause the production of a new layer?
The cells start to pile up on either side of the primitive streak, and when they get to the edges of the streak, they push through the epiblast later and spread throughout the embryonic disc, which displaces the hypoblast and produces a new layer
Is the hypoblast involved in the formation of the new layer?
No
Why is the hypoblast not involved in the formation of a new layer?
It has already done it’s job of lining the primitive yolk sac and forming the secondary yolk sac
What happens to the hypoblast by the end of the gastrulation process?
It has regressed entirely
What are the 3 layers produced by gastrulation?
NAME?
What is the name of the differentiated top layer?
Ectoderm
What is the name of the new middle layer?
Mesoderm
What is the name of the layer that is the replacement for the displaced hypoblast?
Ectoderm