1D - Development(3) Flashcards
What is the blastula of most animals?
Hollow sphere
In birds/reptiles/amphibians, what is the blastula replaced by?
Thin blastodisk, sits on top of blastocele
What is below blastocele?
Non-cellular yolk
What is behind blastodisk?
Yolk
What is underneath blastodisk?
Blastocele
What is the space (middle) of primitive streak called?
Primitive groove (middle)
Who was the first person to study plankton and coin the term primitive node?
Victor Hensen
What is the single-layer tissue that forms blastodisk?
Epiblast
Does tissue in blastodisk move medially toward primitive streak?
Yes, when it gets to primitive streak, it rolls inward and swings laterally
T/F: Cells involute from epiblast and roll inside
True
When tissue rolls inside, what does it form?
Can form endoderm, mesoderm and ectoderm
Frogs and Humans: Side of involution
- Humans have elongated locus of involution (primitive streak).
- Frog site of involution is blastopore
What is the central portion of primitive streak where tissue involutes to form endoderm and mesoderm?
Primitive groove
What is the node at anterior (rostral) end of primitive streak?
Hensen’s node (specialized region of primitive streak)
Hensen’s node in humans is homologous to what structure?
Dorsal lip of blastopore in frogs
In frogs, the very 1st tissue to involute happens at dorsal lip of blastopore, which ends up forming mesoderm of notochord.
Analogous at Hensen’s node. Tissue rolls in, involute tissue moves forward towards the front end of the animal and forms the head process which gives rise to the notochord.
What happens when tissue involutes at Hensen’s node?
Gives rise to notochord
What is the gastrula?
3 layer with gut
What process marks the beginnings of the neural tube formation?
Neurulation
What is gastrocele lined by?
Endoderm
How does the notochord run?
Dorsal
What is the precursor to CNS?
ectoderm thickens, forming neural tube
Where does the thickening of the ectoderm happen?
Above notochord
What is the precursor to CNS/neural tube?
ectoderm thickens, forming neural tube
Dorsal to notochord, neural plate has 2 pronounced folds with deep groove. What happens during the fold stage:
- As the folds come into contact with each other, they form neural crest and neural canal
- as 2 neural folds together, neural groove is trapped inside, cut off completely
What 2 fusions occur?
1) thin surface ectoderm fuses together
2) edges of neural tube itself fuse together
Differentiation of neural plate
- Neural plate differentiates into thinner region of neural groove in middle; thicker regions containing neural folds on either side
- Neural folds get higher
- Neural groove gets deeper
Process of neurulation
- thickening of ectoderm
- neural folds higher, groove deepr
- As the folds come into contact with each other, they form neural crest and neural canal
- Invagination
Invagination gives what?
hollow tube, which is made from tissue that starts off as ectoderm
Why does it occur dorsally?
- Notochord, which secretes chemical messengers to bring about invagination
- Notochord forms first
- Chemical messengers cause ectoderm to thicken to form neural plate
- Cause ectoderm to fold up (invaginate) to seal off and form hollow tube
Early stage of gastrula
- primitive streak forms, retreats gradually back, laying notochord behind it
- notochord induces neural plate and invagination of neural tube
- Rostral –> neural folds and groove invaginate to form tube
Late stage of gastrula
- fusion process complete
- thin surface ectoderm fused together –> continuous alongside back of animal
- thick tissue of neural tube fuse together to give complete tubular structure
How does development occur?
Front to back
Where does neural tube first form?
neck region
Anterior Neuropore
Process of fusion of neural folds where it gives an opening inside of neural tube to outside, running at the front tip of embryo
Posterior Neuropore
back edges of neural folds close
Chick embryo is similar in humans (1)
- remanants of blastodisk floating on tip of yolk
- Ectoderm thickens to form neural plate
(2)
Neural folds are more prominent
Neural grooves deeper
(3)
- Edges of neural folds come together
- Space inside neural groove is cut off
- Invagination (surrounded by complete, thick ectoderm)
Neural crest
- as process of invagination occurs, a bit of tissue is pinched off, does not form neural tube/surface ectoderm
- this tissue gets pinched off between ectoderm and neural tube
Neural crest
- as process of invagination occurs, a bit of tissue is pinched off, does not form neural tube/surface ectoderm
- this tissue gets pinched off between ectoderm and neural tube
- gives rise to PNS
Dorsal/lateral to notochord
Mesoderm thickens to form somite
