2 Development of pharyngeal arches and face

Question 1

At 4 weeks development

Answer 1

frontonasal process (has developing forbrain with it)
- will enlarge in conjunction with NS
No separation between mouth and nose this point (no nasal cavity )

Question 2

4.5 weeks

Answer 2

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
-

Question 3

what does breaking down of the buccopharyngeal membrane

Answer 3

allows continuity between the stomodeum and the foregut

Question 4

what does separation of the nose and mouth involve

Answer 4

1) primary palate and the nasal septum

2) secondary palate and nasal septum

Question 5

what is found at front of frontal nasal process

Answer 5

nasal placode

Question 6

nasal placode

Answer 6

specialised epithelium area

Question 7

what does the nasal placed do

Answer 7

invaginates into frontal nasal process

Question 8

what happens as the frontal nasal process is getting bigger(4.5 weeks)

Answer 8

• 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

Question 9

what is swelling of cells around the placed known as

Answer 9

lateral nasal process

medial nasal process

Question 10

what does the tissue between the medial nasal processes form

Answer 10

primary nasal septum

Question 11

what happens to the nasal place being pushed back

Answer 11

committed into specialised olfactory epithelium

Question 12

what is on the lateral aspect of the head 4.5 wks

Answer 12

lens placode

Question 13

how are the primitive nasal cavities formed

Answer 13

invagination of the nasal placodes forming the nasal pits

Question 14

what is the primary palate (when forming initial)

Answer 14

material left slightly inferior to the primitive nasal cavity

Question 15

what does the primary palate do when forming

Answer 15

starts to separate the nasal cavity from the primitive oral cavity

Question 16

when do the maxillary processes extend from and when and what do they form

Answer 16

5 weeks
from posterior aspect of md arch
form lateral borders of mouth

Question 17

what grows messily from mx arches

Answer 17

two pairs of processes

• superior is the tectoseptal process
• inferior is the palatine process

Question 18

how are the paired processes of mx developed

Answer 18

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

Question 19

what does the palatal process growth dependant on

Answer 19

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)

Question 20

what are the process of the mx arches

Answer 20

nasal pits
nasal septum
palatine processes

Question 21

what happens at 8 weeks

Answer 21

palatal elevaton

Question 22

how does palatal elevate occur

Answer 22

• 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

Question 23

extrinsic factors in palatal elevation

Answer 23

widening of the mandible

movement of the head

Question 24

intrinsic factors in palatal elevation

Answer 24

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

Question 25

what are growth factors regulated by

Answer 25

different transcription factors

Question 26

at 10 weeks..

Answer 26

• all processes have grown to the point where they make contact (mx process, primary palate, nasal septum, palatine processes)
• These need to be in sufficient contact so they can fuse and form the mature structures

Question 27

what does fusion of palatine processs occur with

Answer 27

each other
primary palate
nasal septum

Question 28

what is needed for fusion of palatine process

Answer 28

breakdown of ectodermal covering of processs

• allows underlying ectomeehcnume to merge
• ectomesenchyme releases signals that institute programmed cell death (apoptosis) in ectodermal cells

Question 29

what does ectomesenchyme do (ectoderm(

Answer 29

determines fate of ectoderm

Question 30

steps involved in palatine process fusion

Answer 30

1) Ectoderm is covering the processes
2) There are signalling processes between the epithelium and mesenchyme, Msx 1 is found in the medial edge of the epithelium
3) This regulates the growth factors expressed rom the epithelium into the mesenchyme
4) the mesenchyme then signals back to the epithelium through peptide growth factors causing apoptosis to occur
5) Breaks down the epithelium and allows continuity of the ectomesenchyme to occur
6) starts in the middle of the palatine processes, extends anteriorly and posteriorly
7) takes about 2 weeks to then be fully fused, finished around 12 weeks

Question 31

after palatine processes fused what happens

Answer 31

differentiates over the next 3/4 weeks

• anterior 2/3rd palate invaded by bone, forms the hard palate
• posterior 1/3rd invaded by muscle from the 4th pharyngeal arch to form muscles of the soft palate, therefore innervated by the vagus nerve

Question 32

what can remnants of epithlium in midline of palate do

Answer 32

proliferate pathologically

form cysts in palate

Question 33

formation of the face

Answer 33

1) Frontonasal process is compressed between maxillary processes to form protruding nose
2) fusion of maxillary and mandibular processes to form mouth
3) anterior movement of the eyes, causes pressure on midline structures to become narrower

Question 34

macrostomia

Answer 34

failure of fusion of mx and md processes

Question 35

when can clefts occur

Answer 35

between any internal or external processes

most common is cleft lip

Question 36

how can some clefts be carried

Answer 36

through X chromosome

Question 37

contributing factors to cleft

Answer 37

smoking/alcho
folic acid deficiency
before 12 weeks