Palate Development Flashcards
What weeks does formation of the palate occur?
weeks 6-12
the development of the palate establishes what?
the divide between the nasal cavity and the oral cavity
what fuses together to form the primary palate?
The fusion of the medial nasal prominences creates the inter-maxillary segment which forms the primary palate (anterior 1/3rd of the definitive palate)
what is the definitive (secondary) palate important for?
mastication - bolus formation
sensation - taste and texture
speech
what gives rise to the palatal shelves?
Extomesenchymal cells of the maxillary process migrating in mesially
when do the palatal shelves drop down either side of the tongue?
During week 6/7 the palatal shelves grow medially until they bump into the tongue, where they then drop down either side of the tongue (they do not attach to the tongue)
What week do the lateral palatal shelves filp into a horizontal orientation and what does this depend on?
Depends of gender
Males - sometimes week 7
Females - usually week 8
What withdraws downwards to allow the lateral palatal shelves to filp?
the tongue withdraws down in week 8
What are the extrinsic factor theories as to palatal shelve elevation?
Tongue withdrawal due to
- head lifting from cardiac plate
- meckel’s cartilage growth
- increased height of nasal cavity
(true but cause or facilitate elevation)
What are the intrinsic factor theories for palatal shelve elevation?
- hydration of extracellular matrix - hyaluronan (GAG)
- Mesenchymal cells appear to shorten, contractile microfilaments
- forces directed via collagen fibres
- altered blood flow
By the end of week 8, what is happening?
Towards the end of week 8 we have mesenchyme migrating in, matrix being laid down and epithelial proliferation around the outside
we start to get the beginning of the shelves touching
By the end of week 8 the lateral shelves have grown across the midline and they’re starting to form a secondary palate
The palatal shelves fuse in what direction?
fuse from the front first towards the back
How long does it take for the palatal shelves to fully fuse?
about 4 weeks
What week do we have a fully fused palate (primary palate down the secondary shelves right to the back of the mouth)?
week 12
What are the 2 types of fusion in development?
Non true fusion - removal of a gap from pushing up from a furrow
True fusion - two differenet things fusing together and forming a midline
What type of fusion in palate development
true fusion
Once the two palatal shelves have come together and actually touched, what is the group of cells down the middle called?
midline epithelial cells
Why does the epithelial of the palatal shelves not fuse with the tongue when they bump into each other, but will fuse with each other?
The epithelial cells produce very specific glycoproteins (sticky surface), the ones on the palatal shelve surfaces are different to the ones on the tongue so will not fuse
What are the 3 theories for mid-line epithelial cell disintegration?
1 Epithelial-mesenchymal transition
2 Apoptosis of epithelial cells
3 Migration to the nasal or oral edge
What causes epithelial cell rests?
some of the midline epithelial cells do not migrate/apoptosis or transition into mesenchyme which result in cell rests
What is the problem with epithelial cell rests
Epithelial cells rests have cystic potential which can cause pain in the roof of the mouth
What is it called if the palate fails to fuse (either completely or partially)
Cleft palate
What is a teratogen?
a substance that interferes with normal fetal development and causes congenital disabilities
What are the risk factor for palatal clefts?
Smoking
alcohol abuse
Drugs - both medical and recreational
viruses
rubella
Too much vitamin A (or other retinoids
Deficiencies in folic acid
Are cleft palates more common in males or females?
Females (thought maybe because the fusion process starts later?)
What 3 enzymes synthises HA (Hyaluronic acid)?
HA synthase 1
HA synthase 2
HA synthase 3
What is synthesised by HA synthase 1, HA synthase 2 and HA synthase 3 and found of different chromosomes and expressed different times during development?
HA (hyaluronic acid/hyaluronan)
What two enzymes produce large molecular weight of HA?
HA synthase 1 and 2
What enzyme produces a smaller molecular weight of HA?
HA synthase 3
What HA synthase do you get mainly during early development
HA synthase 2
What is a knock out mouse?
a laboratory mouse in which one or more genes have been turned off or “knocked out. This is to silence the gene of interest
In what knock out mice do you get a cleft palate? What gene is turned off?
TGF beta 3
