Lect 3 Flashcards
What events occur in week three?
Week three is the embryonic period. - 1- gastrulation: forms trilaminar disc 2- neuralation : forms neural tube 3- body folding : embryonic disc folds into more complex shape
What occurs during the embryonic period?
Formation of germ layers and organogenesis
When does gastrulation, neuralation, and body folding end?
Begin week three! End in week 4!
Which cell types are used in gastrulation?
Epiblast
What does gastrulation form?
Three germ layers ( trilaminar disc) using epiblasts only!!
1- ectoderm : outer surface
2- mesoderm: migrating middle
3- endoderm: inner cell layer / displace hypoblast
Where is the site of epiblast invagination ( gastrulation) ?
Primitive node
What are the functions of the primitive node and primitive streak?
Epiblast invagination ; organise layers; determine body axes
Which element is the primary migration organiser? ( during gastrulation)
Primitive node
What is the function and future feature of the oropharyngeal membrane?
On cephalic end/ future mouth
What are the cell migration routes in the trilaminar disc?
Caudal to cephalic ( but get better in cephalic to caudal)
During gastrulation what happens to the epiblast?
Epithelial- mesenchymal transformation
Formation of undifferentiated migratory cells : mesenchymal cells
Epithelial : tightly adhered
Mesenchymal : loose, non adherent
Explain regression of the primitive streak?
Cephalic to caudal development. Migration is caudal to cephalic so the streak remains the same as the remainder of the organism grows. Tissue proliferation extends to the cephalic end. Matures in cephalic to caudal direction
What event contributes to CNS development?
Neuralation ( wk 3-4 )
Where is the notochord located?
The notochord ( used in neuralation) is found at the invagination of the primitive node pit ( going toward to oropharyngeal membrane) migrates along midline and stops at pre chordal plate
What cells surround the amniotic cavity in wk 3
Ectoderm
Endoderm surrounds the sYS
Notochord induces overlaying surface ectoderm to become…
Neuroectoderm
Neural folds develop into what structure?
Neural folds gradually creat neural grove and then the neural tube ( tube right above the notochord) tube is comprised of neuroectoderm
If the rostrum neuropore fails to close properly what can happen?
Anencephaly ( no head development )
What happens when the caudal neuropore fails to close?
Spina bifilar and spina bifilar cystica
What does endoderm give rise to?
Gametes, epithelial cell lining : - GI, Liver, pancreas, respiratory airways, and some urogenetal structures
Which germ layer produces - hair, nails, glands, epidermis, neural crest,
Ectoderm and the notochord induces neuroectoderm
What three diffrentiations of mesoderm are there?
Paraxial ( closest to neural tube) ; intermediate ( middle) ; and Lateral plate ( which yields 2 others - parietal on amniotic cavity side/ and visceral sYS side for organs )
Where do somites originate from?
Somites are from paraxial mesoderm, which is from mesoderm,which is from epiblast cells.
What do somites give rise to?
Sclerotome ( bone); myotome( muscle) and dermatome ( skin)
Develops cephalic to caudal
Which germ layer is responsible for urinary or reproductive issues?
Mesoderm- intermediate mesoderm!
What are the two types of body folding?
Lateral and cephalocaudial ( head to tail)
What drive body folding?
Later BF : driven by growth of somites
Caphalocaudal BF: driven by growth of neural tube
What does the gut tube from from?
Secondary yolk sac! And intraembryonic cavity ( during lateral folding)
How does the primitive mouth and heart get to the adult position?
During cephalocaudial body folding ( longitudinal growth of neural tube)
What happens at end of embryonic period?
Finish - gastrulation/ neuralation/ and body folding ( end of week 4)
Limbs elongate / rotate / face appears
Organogenesis
This period is greatest risk for brith defects
