Gastrulation, Folding and Neurulation Flashcards
What is the depression at one end of the embryo?
Future mouth
What is the primitive streak important for?
Driving gastrulation
How many germ layers does gastrulation give rise to?
3
Where is the primitive streak found?
Midline at the caudal end of epiblast
What is found at the cranial end of the primitive streak?
Primitive pit and node
Describe how 2 germ layers become 3
Cells lose attachments with others and migrate to primitive streak and dive down through it, this pushes epiblast and hypoblast apart
What is the endoderm layer made up of?
Hypoblast cells and new cells from primitive streak
What is the mesoderm layer made up of?
Migrating cells that push original cells apart
What is the ectoderm layer made up of?
Original cells/left over cells
What is the hypoblast replaced by?
Definitve endoderm
What is the epiblast replaced by?
Ectoderm
What layer forms between endoderm and epiblast?
Intraembryonic mesoderm
What is the cloacal membrane?
Future anus
What cells form the future notochord?
Cells that migrte through the node itself
Describe the notochord process
Cells migrate throughthe primitive pit form a hollow mdline tube that extends cranially
As the notochord moves down, what does it come into contact with?
Endoderm layer
How does the notochord become a solid rod?
It loses connection with the endoderm and moves into the mesoderm layer
Where can the notochord diffuse into?
Either side of the intermesoderm layer, ectoderm layer or endoderm layer
After folding occurs, what happens to the ectoderm?
Gives up most of the outer layer of skin and nervous system (which starts at the epidermis of skin then sinks down into body)
After folding occurs, what happens to the mesoderm?
Divides into 3 distinct groups: paraxial; intermediate; lateral (somatic and visceral)
What is the paraxial mesoderm?
2 rods either side of the notochord on midline axis
What is the lateral mesoderm?
Divides into somatic (associated with ectoderm) and visceral (associated with endoderm)
What does the paraxial mesoderm contribute to?
Forms all vertebrae; some parts of brain; sternum; all voluntary muscle (bar head and neck); deeper layer of skin (dorsal midline dermis)
What does the intermediate mesoderm contribute to?
Urogenital systems (ducts of gonads; gonads; kidney; ureter)
What does the somatic mesoderm (lateral plate) contribute to?
Lining of body wall; most of dermis (bar back); skeletal elements of limbs
What does the visceral mesoderm (lateral plate) contribute to?
Cardiovascular system (blood vessels and heart); mesotheial covering of organs; smooth muscle of organs
What does the endoderm contribute to?
Lining of gut tube; lining of respiratory tract; lining of bladder and urethra (cloacal has divided into 2 parts)
What are the 2 parts the cloaca divides into?
Posteriorly contributes to bladder and urethra; and anteriorly contributes to rectum and naus
What surface is the neural plate found on?
Dorsal
What happens to the primitive streak at the end of week 3?
It regresses
What cells form neural plate?
Cells within ectoderm
When ectoderm cells receive a signal from the notochord, what occurs?
They begin to differentiate towards a neural lineage
How does the nervous system become protected?
The tissue needs to come into the body of the embryo; so the neural playe begins to fold in on itself; edges rise up and pull ectoderm witht it
During day 20, what is more pronounced?
Neural groove/fold
What occurs on day 22 of neural tube formation?
This is the first point of closure as edges of neural plate fuse and ectoderm fuses over the top
What end closes first; cranial or caudal?
Cranial
What day do the cranial/anterior neuropores close?
Day 24-25
What day do the caudal/posterior neuropores close?
Day 26-28
Where are neural crest cells found?
Between neural plate and ectoderm (they break and migrate)
What ganglia has cells from neural crest?
Dorsal root; sympathetic; aortic gangli; ganglia of gut tube
What releases hormones derived from neural crest cells?
Suprarenal gland
What do neural crest migrations give rise to?
Non-neural structures (skin pigment cells)
What are the neural crest derivatives?
Septum outflow of heart; bones of skull; eyes; cranial nerve ganglia; teeth; schwann cells
