2 Development of pharyngeal arches and face Flashcards
At 4 weeks development
frontonasal process (has developing forbrain with it) - will enlarge in conjunction with NS No separation between mouth and nose this point (no nasal cavity )
4.5 weeks
formation of nasal cavity and primary palate
- maxillary process grows out of the mandibular process
both innervated by 5th CN
- important step in separating the palate from the nose and forming the lateral borders of the mouth
buccopharyngeal membrane breaks down
-
what does breaking down of the buccopharyngeal membrane
allows continuity between the stomodeum and the foregut
what does separation of the nose and mouth involve
1) primary palate and the nasal septum
2) secondary palate and nasal septum
what is found at front of frontal nasal process
nasal placode
nasal placode
specialised epithelium area
what does the nasal placed do
invaginates into frontal nasal process
what happens as the frontal nasal process is getting bigger(4.5 weeks)
- proliferation is less around the placode
- therefore burys inside the frontal nasoprocess
- cells proliferate around the placode causing ridges
- further makes the placode appear to be tunnelling into the embryo
what is swelling of cells around the placed known as
lateral nasal process
medial nasal process
what does the tissue between the medial nasal processes form
primary nasal septum
what happens to the nasal place being pushed back
committed into specialised olfactory epithelium
what is on the lateral aspect of the head 4.5 wks
lens placode
how are the primitive nasal cavities formed
invagination of the nasal placodes forming the nasal pits
what is the primary palate (when forming initial)
material left slightly inferior to the primitive nasal cavity
what does the primary palate do when forming
starts to separate the nasal cavity from the primitive oral cavity
when do the maxillary processes extend from and when and what do they form
5 weeks
from posterior aspect of md arch
form lateral borders of mouth
what grows messily from mx arches
two pairs of processes
- superior is the tectoseptal process
- inferior is the palatine process
how are the paired processes of mx developed
1) Tissue proliferates both superiorly and inferioally
2) Superior is the tectotsepal process, inferior is the palatine
3) Tectoseptal process grows horizontally, palatine extends inferiorly on the lateral borders of the tongue
4) tectoseptal forms structures on the base of the skull
5) Then starts to extend inferiorly, this dangly tissue forms the nasal septum
6) The growing palatine processes extend laterally either side of the tongue until it reaches a considerable proportion of the embryonic mouth
7) cells in the palatine processes being to proliferate more, secrete more ECM
what does the palatal process growth dependant on
1) FGF10 is expressed in ectomesenchyme (neural crest derived cells)
- acts on FGF2R in ectodermal covering
2) FGF10 -/- mutation leads to no or reduced growth of palatine processes (loss of the FGF leads to this)
what are the process of the mx arches
nasal pits
nasal septum
palatine processes
what happens at 8 weeks
palatal elevaton
how does palatal elevate occur
- innervation of the palatal shelfs occur, move from vertical and lateral to tongue to lateral and superior to the tongue more like normal anatomical
- The embryo develops a cervical flexure, lifting the head away from the cardiac bulge
- the mandible widens allowing the tongue to drop into the floor of mouth, creates space more superiorly for the developing palate
- palatal processes now have no restraint and elevate into a horizontal position
extrinsic factors in palatal elevation
widening of the mandible
movement of the head
intrinsic factors in palatal elevation
agents that disrupt GAG (glycosaminoglycan) synthesis tend to inhibit palatine elevation
- hyaluronic acid accumulates around the ectomesenchyme within the processes
- bonds to large amounts of water
- increases turgor inside the palatine processes
- as water is sucked in leads to inflation, causing them to flip up
