Early Embryonic Development Flashcards
What are cleavage divisions?
Mitotic cell divisions in early embryos
What are cells of the cleavage divisions called?
Blastomeres
What determines cleavage in most animals?
Amound and distribution of yolk
Two types of cleavage patterns
Holoblastic
Meroblastic
Explain Holoblastic
Furrow completely cuts through embryo
In what type of embryos does holoblastic cleavage occur?
This occurs in embryos with moderate (amphibians) to little yolk (mammals) and can be unequal or equal
What is meroblastic?
Incomplete cleavage divisions
What type of embryos is meroblastic found?
Embryos with lots of yolk
- Fish
- Reptiles
Are cleavage divisions synchronous or asynchronous in mammals?
Cleavage divisions are asynchronous in mammals
In mammals when is pre-implantation development?
Period of embryonic development from fertilization to just prior to implantation
What is the zona pellucida?
Glycoprotein containing extracellular matrix surrounding the oocyte and early embryo
When does embryonic genome become activated?
During early cleavage stages
What is morphogenetic event 1?
Compaction
What occurs duing morphogenetic event I: Compaction?
Unique event that begins after 3rd cleavage
Cells huddle closely togeth and form compact ball at 8cell stage
Just prior to and durring compaction, blastomeres become polarized
What occurs just prior to and during compaction to blastomers?
Blastomeres become polarized
Start to see presence of microvilli
What is the 16-cell stage referred to as?
Morula
What do the outside cells do during Morphogenetic Event I :Compaction?
Form tight permeability seal with tight junctions, desmosomes, and adherens junctions
What do cells on the inside do durring Morphogentic Event I: Compaction?
Become connected by gap junctions
What do the outside cells of the morulae destined to become?
Trophectoderm and the trophoblast
ie., extraembryonic lineage
What do the inner cells of the morulae do durring Morphogenetic Event I: Compaction?
The inner cells will derive the embryo by first forming the inner cell mass (ICM
What is Morphogenetic Event II also known as?
Cavitation
What occurs durring Cavitation?
Fluid begins to accumulate in the compacted morulae forming small vessicles
The vessicles coalesce into a blastocoel and the embryo becomes a mammalian blastula known as a blastocyst
What is a primary driver of Cavitation?
Enzyme NaK-ATPase
What does NaK-ATPase do during cavitation?
Pumps 3 Na into cavity and 2K out
Creates an osmotic gradient to allow H2O to fill blastocoel
What is Morphogenetic Event III also known as?
Blastocyst Expansion
Primary driver of Morphogentic Event III: Blastocyst Expanison
NaK-ATPase
Why is Morphogenetic Event III: Blastocyst Expansion essential?
Culminates in the first differentiative event
What is the first differentiative event
Differentiation of
ICM
- Embryo proper
Trophectoderm
- Extraembryonic lineages
What occurs with blastocyst expansion?
Hatching
What does hatching prepare for?
Implantation
At hatching what does the ICM differentiate into?
Hypoblast
Epiblastt
What effect does blastocyst expansion have on the zona pellucida?
Weakens it
What 3 forces govern hatching?
- Growth and fluid accumulation within the blastocyst
- Production of enzymes by the trophectoderm cells to break down the matrices comprising zona pellucida
- Contraction of the blastocyst
