palatal development Flashcards
function of soft palate
Closes off nasal passages during swallowing
Protects the nasal cavity during sneezing
Involved in speech and sounds
function of hard palate
Separates the nasal cavities from the oral cavity
Important for mastication and speech
Ridges (rugae) help movement of food towards pharynx
how is the primary palate formed?
- mesial growth of the maxillary processes towards nasal processes
- is not able to fuse due to nasolacrimal and bucconasal grooves
- mesial nasal processes grow towards each other and merge
- forms philtrum
- forms region of maxilla carrying incisor teeth
- forms primary palate
- fusion between the maxillary process and lateral aspects of the medial nasal processes = lateral aspect of upper lip
what prevents the fusion of the primary palate?
Fusion is prevented by the nasolacrimal and bucconasal grooves.
when does the secondary palate become visible?
when does the development of the secondary palate begin?
As the medial nasal processes and maxillary prominences fuse the primary and secondary palates become visible as outgrowths.
- begins at the 6th week of gestation (or E13.5 in mice) and completes in the third month
- Week later in females
what is the importance of the secondary palate and it’s fusion?
Development of secondary palate is required to separate the nasal and oral cavities
- oronasal cavity mainly occupied by the tongue
The secondary palate composes more than 90% of the hard and soft palates
what are the palatal shelves?
mesenchyme (neural crest) surrounded by a thin layer of oral epithelium
what regulates palatal outgrowth?
- Shh
- FGF-10 -
- receptor is FGFR2b
- Positive feedback loop
how does BMP regulate palatal outgrowth?
- crosstalk between Shh and BMP signalling
- Smo is transmembrane receptor required for Shh signalling
- decreased Smo = increased BMP4 and decreased BMP2
- BMP2 is a positive regulator of mesenchymal cell proliferation
- decreased Smo = increased BMP4 and decreased BMP2
how occurs when there is disruption of signalling?
give rise to cleft lip and palate
(reduction in anterior palatal mesenchymal cell proliferation)
how do matrix proteins regulate palatal outgrowth?
ADAMTS = family of enzymes (metalloproteinases)
- Bind to cell surface and degrade (proteolysis) extracellular matrix components
Disruption in genes encoding for ADAMTS 9 and 20 result in cleft palate
hoes does palatal shelf elevation take place?
when does it occur?
at week 8 of gestation
- palatal shelves elevate to horizontal position above tongue
- rapid
what are the theories for palatal shelf elevation ?
Rapid rotation of the shelves (Walker and Fraser 1956)
Growth based regression of distal region and outgrowth in horizontal direction (Lazzaro 1940)
why do the palatal shelves elevate?
Ferguson (1981) proposed that the shelves initially grow vertically due to space restraints in the oronasal cavity
- tongue
what extrinic forces are there in palatal elevation?
Downward movement of the tongue - mandibular growth spurt
Downward displacement of the tongue by the nasal septum
Lowering of the tongue due to a foetal mouth opening reflex
Physical pushing of the shelves upwards by the tongue
