prenatal craniofacial development Flashcards
what happens during the 4th week
ventral mesoderm condenses into a series of segmented bilaterally paired, mesenchymal swellings
initially FIVE prominences (tissue masses) surround the stomodeum
these are
frontonasal prominence
first arch (> mandibular process)
maxillary process (delayed appearance)
first (mandibular) arch and maxillary processes are both paired structures that grow
ventro-laterally around the OM (oropharyngeal membrane aka back of the mouth)
the majority of the growth and morphological change in facial tissue masses is driven by the invading
cranial neural crest-derived mesenchyme
maxillary processes originate
as separate (delayed) swellings rostral to the mandibular processes
invaded by distinct population of late migrating CNCC
the thickening of ectoderm in FNP (frontonasal prominence)
nasal placodes
two types of morphological processes for joining tissues
- merging: joining of two masses already partly in contact
- fusion: joining of two separate masses
two examples of merging
- merging of maxillary (MXP) and lateral nasal processes (LNP)
- medial merging of mand (MNP)
two examples of fusion
contact dependent fusion between MNP and MXP/LNP
MNP with MNP
MNP with MXP
MNP with LNP
another fusion event is with the secondary palate (future roof of mouth) during 10th week which arises later from the
medial aspects of the MXP >palatal shelves
(fusion event)
after immigration of cranial neural crest cells, growth and morphogenesis of the face is controlled by
ongoing epithelial-mesenchymal interactions
(controlled independently)
these cells primarily determine facial form/shape
cranial neural crest cells
neural expression of ______ precedes and required for the ectodermal expression
Shh/Fgf8
Shh= ventral facial ectoderm
Fgf8= dorsal facial ectoderm
secreted factors from the ____ can direct outgrowth of the underlying CNCC and determines D-V pattern of FNP.
But precise shape depends upon pattern information inherent in the _______
frontonasal ectoderm zone (FEZ)
neural crest
the ectoderm has a role and supports/directs =
and guides=
and facilitates=
outgrowth of the facial processes and
guides differentiation of CNC
and facilitates timely fusion of the facial processes
when does secondary palate form
10th week
(forms well after the primary palate/lip) 7th week
what determines secondary palate formation:
1
2
3
- growth (either side of the tongue)
- elevation and rotation
- medial growth and fusion at midline with nasal septum
ossification of the secondary palate (osteoblasts derived from CNCC) begins
just before palatal development complete
what is the secondary palate
palatal shelves (condensations of CNCC mesenchyme)
how can cleft secondary palate result from
- poor growth of shelves
- failed elevation
- failed fusion
what is critical to allow the shelves to rotate to a position above the tongue
tongue lowers
this can provide a physical barrier to secondary palate closure
macroglossia
this also is associated with failed palatal fusion where the tongue sits too far back aka tongue forced backwards and elevated
small or retrognathic mandible
this first appears in the mandible and shortly thereafter in the midface and cranial base. provides structural support for shaping the growing head!
craniofacial cartilage
