Development of trilaminar germ disc Flashcards
How many germ layers are in the trilaminar germ disc?
3
What structure is the trilaminar germ disc derived from?
Bilaminar germ disc
What is the first structure that forms in the development of the trilaminar germ disc?
Primitive streak
What is the primitive streak?
Linear band of epiblasts in caudal end of bilaminar germ disc that consists of structures primitive node, groove, pit
How does the bilaminar germ disc change shape, and what regions does it contain?
Elongates to become oval-shape, wider end is cranial region and narrower end is caudal region
What direction does the primitive groove run in?
Caudally from midline
How does the primitive node form?
Cranial end of primitive streak deepens
What structure is within the primitive node, and what shape is it?
Primitive pit, which is a circular depression
Which direction of primitive pit run in?
Runs continuously with primitive groove
What body axis is determined by the primitive streak?
Cranial-caudal axis
After the primitive streak is complete, what process occurs?
Ingression
What is ingression?
Movement of epiblast cells through primitive streak and into interior of embryo
When epiblasts migrate into primitive streak during ingression, what transition progress do they undergo?
Epithelium-to-Mesenchymal Transition (EMT)
How is the structure of epithelial epiblasts different to the structure mesenchymal epiblasts?
Epithelial: tightly connected, regularly shaped, cuboidal
Mesenchymal: loosely connected, irregularly shaped, bottle-shaped
What layer in the trilaminar germ disc do the first mesenchymal epiblasts form and how?
Mesenchymal epiblasts replace hypoblast to become endoderm
After the endoderm has formed, what do the next ingressing mesenchymal epiblasts form in the trilaminar germ disc?
Migrate in between epiblasts and endoderm to form mesoderm
After most epiblasts have ingressed, what do the remaining epiblasts form in the trilaminar germ disc?
Ectoderm
What are the 4 types of mesoderm that are formed?
Paraxial, head, intermediate, lateral plate
Where is paraxial mesoderm found?
Head and trunk region, lateral to notochord process
How does head mesoderm form?
Paraxial mesoderm in the head region
What does paraxial mesoderm form in the trunk region?
Somites
What system does intermediate mesoderm form?
Urogenital
What system does lateral plate mesoderm form?
Gastrointestinal, body wall
