Prenatal Craniofacial Development Flashcards
Morphogenesis of the face is a complex 3D process involving…
patterning, outgrowth, fusion and moulding of tissues
At 22 days, the head and neck region comprise ____ of the embryo
1/2
During 4th week, ventral mesoderm condenses into a series of segmented bilaterally paired, mesenchymal swellings called…
pharyngeal (branchial) arches
How many pairs of pharyngeal arches are there?
5 pairs
What does the first arch make?
mandibular process
When does the oropharyngeal membrane break down?
during 4th week
First (mandibular) arch and maxillary processes are both ______
paired structures
- grow ventro-laterally around the OM
The majority of the growth and morphological change in facial tissue masses is driven by the…
invading cranial neural crest-derived mesenchyme
The paired first pharyngeal arches only give rise to the _______ processes
mandibular
(his slide is funky and i hate it)
Where do the maxillary processes originate from?
separate (delayed) swellings rostral to the mandibular processes
- distinct population of late migrating CNCC
Formation and invagination of nasal placodes (thickening of ectoderm) in…
Frontonasal Prominence (FNP)
What is the induction and invagination of nasal placodes similar to?
neural plate induction & invagination
What are the two types of morphological processes for “joining” tissue?
- merging
- fusion
What is merging?
joining of two masses already partly in contact
What is fusion?
joining of two separate tissue masses
How do the maxillary (MXP) and lateral nasal processes (LNP) come together?
merging
How do the medial nasal processes and maxillary (MXP)/lateral nasal (LNP) come together?
fusion
What does the medial nasal processes and maxillary (MXP)/lateral nasal (LNP) form together?
primary palate and nares (nostrils)
In what week do the medial nasal processes and maxillary (MXP)/lateral nasal (LNP) fuse together?
6th week
What does the secondary palate arise from?
the medial aspects of the MXPs > palatal shelves
When does the secondary palate arise?
10th week
After immigration of cranial neural crest cells, growth & morphogenesis of the face is controlled by ongoing…
epithelial-mesenchymal interactions
*dont need the rest of the embryo
What cells primarily determine facial form/shape?
Cranial neural crest cells (CNCC)
There are ______ boundaries of expression in facial ectoderm
defined
Neural expression of ______ precedes (and is required for) the ectodermal expression
Shh/Fgf8
Secreted factors from the FEZ can direct outgrowth of the underlying CNCC and determines D-V pattern of the
Frontal nasal process (FNP)
- but precise shape depends upon pattern information inherent in the neural crest
Transplanted ectoderm retains ______ pattern of expression from originating tissue
FGF8/SHH
What does the dynamic ectoderm do?
- support and direct outgrowth of the facial processes
- guides differeniation of CNC
- facilitating timely fusion of the facial processes
Fusion of the facial processes establishes what?
primary palate and goes on to form the alveolus and lip proper
- full fusion is required to ensure the alveolar bone is continuous
What is the third most common birth defect?
cleft lip
What must occur for secondary palate formation?
- growth (either side of tongue)
- elevation and rotation
- medial growth and fusion at midling with nasal septum
Ossification of the secondary palate begins just before…
palatal development complete
What are the palatal shelves made of?
condensations of CNCC mesenchyme
Secondary palate forms well after the…
primary palate/lip (around 10th week)
What can cause cleft secondary palate?
1) poor growth of shelves
2) failed elevation
3) failed fusion
It is critical that the ______ lowers to allow the shelves to rotate to a position above it
tongue
What can provide a physical barrier to the secondary palate closure?
macroglossia (enlarged tongue)
What is indirectly associated with failed secondary palate fusion?
small or retrognathic mandible (tongue is forced backward and elevated)
- such as Pierre-Robin sequence
Craniofacial cartilage first appears in the ________ and shortly thereafter in the midface and cranial base
mandible
What provides structural support for shaping the growing head?
craniofacial cartilage
The Meckel’s cartilage arises during ___ week
7th
- forms the template for the mandible
What pharyngeal arch is meckels cartilage from?
PA 1
What does PA 1 make besides Meckel’s cartilage?
two ear ossicles (parts of the malleus and incus)
Like most facial cartilages, most is/is not converted to bone?
is not
How does most of the facial cartilage become bone?
parts degenerate
Is the ear formed from independent or dependent embryonic structures?
independent
External and middle ear derivatives of which pharyngeal arches
PA1 and PA2
- intervening pharyngeal cleft & pharyngeal pouch
Inner ear arises from…
thickening of ectoderm (otic placode) dorsal to PA3 at level of hindbrain and subsequent invagination (otic pit)
Inner and outer ear malformations often associated with __________ defects
mandibular
