What is the name of the process by which the intreembryonic mesoderm forms?
What larger process is it the 1st step of?
What triggers it?
Gastrulation - bilaminar > trilaminar disc
- 1st step of morphogenesis the development of bodily form
- triggered by Bone Morphogenetic Proteins (BMPs)
What are the 3 main steps of gastrulation?
- Primitive Streak Formation
- Germ Layer Formation
- Notochord Formation
How/when does the primitive streak form?
Include all the parts of it.
Beginning of 3rd week:
- epiblast cells proliferate and migrate to median plane caudocranially
- cranial end proliferates more to form primitive node
- primitive groove + pit form in streak + node (respectively) via epiblast invagination
When does the primitive streak eventually disappear?
end of 4th week
How do the germ layers of the trilaminar disc form?
(Special kinds of cells, signal molecules, movements, etc.)
epithelial-to-mesenchymal transition (EMT) occurs to epiblast cells via FGF8
mesenchymal cells migrate downard and become mesoblast
TGF-B induces mesoderm formation from mesoblast
- mesenchymal cells displace hypoblast to form endoderm and epiblasts become ectoderm
What happens to the shape of the embryo during gastrulation?
as primitive streak + notochord form it moves through 3 general shapes
What is the acronym for notochord formation?
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- Process - prim. pit invaginates > notochordal process
- Canal - pit extend to form notochordal canal
- Fusion - noto. process floor fuses with endoderm
- Degeneration - holes form in fused layers btwn canal + yolk sac
- Plate - holes fuse, floor disappears, roof = notochordal plate
- Infolding - noto. plate infolds cranio-caudally to form notochord
- Neurenteric Canal - neur. canal briefly remains at site of prim. pit
- Detachment - notochord fully detaches from endoderm and remains in mesoderm
What appears around day 16 in the caudal wall of the yolk sac?
What are its functions?
What does it become?
allantois - diverticulum of yolk sac > connecting stalk
- remains small in humans b/c its respiratory/urinary functions done by placenta + amniotic sac
- involved in early blood formation + development of bladder
- becomes urachus + median umbilical ligament
- its vessels become umbilical arteries + veins
What are some of the derivatives of the ectoderm?
- sensory epithelia
- otic + lens placodes
What are the derivatives of the endoderm?
- GI epithelium
- Glands of GI (liver, pancreas)
- Resp. epithelium
- Tympanic Epithelium
- Thyroid Gland
GGRTTTh - Growth
What are some derivatives of the mesoderm?