Gastrulation- Amphibians Flashcards
What kind of egg is a frog egg- with respect to the yolk?
Mesolecithal: moderate amount of yolk
What does NOT occur in cleavage?
Cell growth
-Cleavage is cell division without cell growth
Frog cleavage is-?
Holoblastic- complete
unequal- due to the distribution of yolk
Radial
What slows down the process of cellular division in some areas of the cell?
The more yolk that cell has the slower it will divide because the yolk is so dense
What is the process of cellular clevage?
-The cytoskeleton constricts the membrane to create a furrow
-A new membrane forms which extends the furrow
How is the blastocoel formed?
Cavitation
-Na+ is pumped into the cell which causes water to follow
-Hydrostatic forces create cavities within the cell
What are the three processes that drive gastrulation?
- Invagination
- Involution
- Epiboly
What occurs in invagination?
- Endoderm cells alter their shape into bottle cells and form a slit in the embryo
- The slit elongates into a circle creating the blastopore
What occurs during involution?
The mesoderm and the endoderm move from the surface of the embryo to the inside of the embryo
What occurs during epiboly?
The ectoderm spreads around the surface of the embryo and allows the blastopore to become the yolk plug
What forces drive invagination?
-Cell shape change involved in bottle cell formation
-Apical constriction
-Cell elongation
What forces drive involution?
-Cell migration of involuted cells
-Radial cell intercalation
-the pre-involuted portion pushes into the blastopore
-Mediolateral cell intercalation
-the post-involuted portion pushes the other cells to the other side
What is convergent extension?
-Occurs during involution with mediolateral cell intercalation
-a ring of mesoderm forms into a ring and gets extended
Are the bottle cells and endoderm at the inner lip of the blastopore passive or active?
-Passive
-they are pulled by cell behaviors around them
