Development II Flashcards
Define Gastrulation and what does it tranform what into
Gastrulation is the coordinated cell and tissue movement where the single layer of the blastula becomes a multi-layered structure known as the gastrula
Gastrulation results in 3 layers name and describe what these layers then form
Ectoderm- epidermis and nervous system
Mesoderm - muscle , skeleton , blood heart etc
Endoderm - digestive tract + organs lungs, pancreas and liver
What are the 3 types of gastrulation movements ?
Ingression , Invagination and Involution
Describe ingression Hint ( what migrates from and to , what thickens , what ingresses into blastocoel ?)
-Migration of individual cells from surface to interior
-Vegetal pole thickens to form vegetal plate
-Primary mesenchyme cells ingress into blastocoel
Describe Invagination - hints: what thickens , how does bucking occur , how does the pseudopodia form , what fuses with the animal pole
- The vegetal plate thickens and invaginates
- Buckling is caused by apical contraction (axin-myosin microfilaments)- this forms the archentron
- Secondary mesenchyme cells form at the tip, producing a pseudopodia pulling the archentron towards the animal pole
The archentron fuses with the animal pole to form a continuous tube .. later on would form the gut - blastopore forms the anus
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What force pulls the tube ( archentron ) toward the animal pole ( opposite of blastopore ) - part of invagination
Elongation by convergent extension - requires integration of lateral lamellipodia causing them to converge
- The archentron narrows causing the elongation for invagination to occur
Describe involution
-Blastmeres on the outside of the blastula migrate inside and up- folds in wards
-This process is similar to invagination
The implantation of the fertilised egg occurs first before gastrulation
Describe the process of implantation ( what will the inner cell membranes divide into and describe them )
The fertilised egg attaches to the uterine wall - the trophoblast proliferates
The trophoblasts proliferates to form the syncytiotrophoblast ( highly invasive tissue that invades the uterine wall - this contains no cell membranes )
The inner cell membranes divide into the epiblast and the hypoblast
The epiblast is what will form the embryo
The hypoblast is what will form Heuser’s membrane - “yolk”
Describe ingression that occurs in Mammalian gastrulation
The epiblast migrate through the primitive streak as individual cells
- the ingressing cells form the embryonic mesoderm
- displaced cells by ingression form the endoderm
-what remains in the epiblast would form the ectoderm
Describe mesoderm formation ( by ingression ) - where do cells ingress throough what do they form
Cells ingress through the primitive streak
They condense at either side of the notochord forming the paraxial, intermediate and lateral plate mesoderm
What does the paraxial mesoderm form ? where does it form and what does it further divide
The paraxial mesoderm forms pairs of somites at either end of the neural tube
- somites futher divide into sclerome, myotome and dermatome( think of these layers of somite )
The sclerome, myotome and the dermatome are parts of the somites
What do these form?
The sclerome forms the axial skeleton
The myotome forms the skeletal muscle
The dermatome forms the connective tissue between the dermal layer of the dorsal skin
What is neurulation and when does it occur ?
Neurulation causes the closure of the neural tube after gastrulation
Describe the process of neurulation ( what elongates to form what ? this causes what to shorten ? what type of movement facilitates this ? )
The neural plate elongates to form the pseudostratified columnar epithelium
this causes the primitive streak to regress// shorten
This is done by apical constriction ( just like involution )
What is the neural crest? what forms this?
The neural crest are multipotent stem cells
- the dorsal roof of the neural tube forms this
