Miscellaneous gastrulation, trilaminar embryo, primitive body cavity Flashcards
The epiblast gives rise to _______
all three primary germ layers
The primitive streak forms in the ______
epiblast
Cells come off of the primitive streak to form the ______
mesenchymal cells that form the mesoderm and endoderm (push into the hypoblast)
The axial area of mesoderm forms the ______
notochord
The primitive streak is at the (caudal, rostral) end of the embryonic disk
The primitive streak is at the caudal end of the embryonic disk (by the connecting stalk!)
What forms at the rostral end of the notochord?
An area of mesoderm at the rostral end of the notochord becomes the PROCHORDAL mesoderm
What forms at the sides of the axial mesoderm?
At the sides of the notochord, there is PARAXIAL mesoderm, which will become the somites.
Then intermediate mesoderm, which will be nephrogenic.
Then the LATERAL PLATE mesoderm, which will become SOMATIC and SPLANCHNIC mesoderm, forming the linings of the body cavities.
What is the clinical significance of the bizarre neurenteric canal?
-> neuroenteric cysts
The primitive streak is a (temporary, persistent) structure
primitive streak is temporary (gone by end of 4th week)
What is the clinical significance of a persistent primitive streak?
If the primitive streak persists, it continues to give rise to all 3 germ layers -> sacrococcygeal teratoma!
There are 2 places where the ectoderm and endoderm meet and mesoderm does not migrate to. What are they?
Oropharyngeal membrane
Cloacal membrane
What is the allantois?
What will it become?
allantois is a diverticulum of endoderm and will become the urachus of the bladder
What will the neural plate become?
Becomes neural tube, which becomes CNS
What will the neural crest become?
Becomes PNS
What will the neural canal become?
Becomes where CSF circulates (ventricles, central canal of spinal cord)
The neural tube first forms in the middle (zippers together from the middle toward the rostral and caudal ends). It remains open at both ends for a while.
What are these open ends called?
The rostral and caudal NEUROPORES
What if the rostral neuropore fails to close?
Neural tube defects like anencephaly and exencephaly
What if the caudal neuropore fails to close?
Neural tube defects like spina bifida
Name 4 derivatives of ectoderm
- skin epidermis (mesoderm -> dermis), hair, nails, subcutaneous glands
- nervous system - CNS, PNS (from neural plate/tube and neural crest)
- sensory epithelia of ear, nose, eye
- branchial (pharyngeal) arches = gill arches -> muscles of head and neck
How is the Intraembryonic Coelom initially created?
The LATERAL PLATE MESODERM (on each side/rim of embryonic disc) cavitates swiss-cheese style, then the holes fuse, forming the first cavity inside the embryo
What does the dorsal (upper) half of the lateral plate/IEC wall form?
Forms the SOMATIC (parietal) MESODERM -> parietal linings of body cavities
What does the ventral (lower) half of the lateral plate/IEC wall form?
Forms the SPLANCHNIC (visceral) MESODERM -> visceral linings of body cavities
What happens with the prochordal mesoderm?
- Prochordal mesoderm spreads rostral to the OP membrane
- Cavitation of lateral plate mesoderm forming IEC splits the prochordal mesoderm into dorsal/somatic (upper) and ventral/splanchnic (lower) halves
- Splanchnic prochordal mesoderm under the IEC (which is passing in front of OP membrane) forms angiogenic cells
- Angiogenic cells coalesce into a solid tube
- The solid tube of angiogenic cells canalizes and forms a pair of hollow endocardial tubes
What does the pair of hollow endochordial tubes become?
Forms the inner lining of the heart
