CFD7 - Palatogenesis: the formation of the palate

Question 1

when is the palate formed?

Answer 1

weeks 6-12

Question 2

when palate forms, what is initially common?

Answer 2

oro-nasal cavity

Question 3

what does the primary palate demarcates?

Answer 3

oral vs nasal components

Question 4

what is the primary palate derived from?

Answer 4

fused medial nasal prominences (part of FNP) - inter-maxillary segment

Question 5

what occurs at the 8th week?

Answer 5

Ossification centres palate around the perpendicular plate

Question 6

what type of ossification is it?

Answer 6

intramembranous ossification

Question 7

what is intramembranous ossification?

Answer 7

Mesenchymal cells  –>osteoblasts
Osteoblasts deposit osteoid….
Mineral deposited
Osteoblasts trapped –> osteocytes

Question 8

what is the role of the definitive (secondary) palate and whats it important for?

Answer 8

- separates the nasal airway + oral cavity 
 Important for:
-Mastication –> bolus formation 
– sensation -> taste and texture
 – speech

Question 9

what does mesenchyme do?

Answer 9

starts proliferating and laying down matrix and so cells push forward to form oral cavity

Question 10

what direction does the palatal shelves grow and why ?

Answer 10

• Grows down the sides

- tongue occupies a large proportion of the ora-nasal cavity

Question 11

Does the mesenchyme attach to the side of the tongue?

Answer 11

NO-

glycoproteins on the tongue do not allow these structures to fuse

Question 12

why are lateral palatal shelves vertically orientated?

Answer 12

insufficient space due to large tongue

Question 13

what happens when the tongue withdraws downwards?

Answer 13

Gives space for shelves to elevate and flip into horizontal orientation
(has to twist as it flips, happens at the same time on both side)

Question 14

what happens to form secondary palate?

Answer 14

Lateral Palatal Shelves contact each other at the midline to form the definitive or secondary palate (week 8)(also connect the nasal septum)

Question 15

Give overview of palatal shelf elevation.

Answer 15

 Initially palatal shelves develop:
– medially
– downwards
 Then palatal shelves:
– rapidly elevate
– grow towards each other

Question 16

what causes palatal elevation?

Answer 16

Forces extrinsic to the palate (Involving the tongue)

 Intrinsic forces generated within the palate

Question 17

Describe the extrinsic factors.

Answer 17

 Tongue withdrawal due to:
– Head lifting from cardiac plate
– Meckel’s cartilage growth
– increases height of nasal cavity.

Question 18

Describe the intrinsic factors.

Answer 18

 Hydration of extracellular matrix:
– Hyaluronan (GAG)
– bind 10x its weight in water –> turgidity
– Hyaluronan accumulates prior to elevation

Question 19

when does amount of water that the GAG binds increase?

Answer 19

during palatal shelf elevation

Question 20

what are other theories for palatal shelve elevation?

Answer 20

 Mesenchymal cells:
– mesenchymal cells appear to shorten
– Contractile microfilaments

 Forces directed via collagen fibres??
 Altered blood flow

Question 21

How does the palatal shelves fuse?

Answer 21

sup up from front to back -between 8 and 12 (over 4 week period).

Question 22

what type of fusion is it when palatal shelves fuse?

Answer 22

true fusion

Question 23

Describe epithelial adhesion .

Answer 23

• sticky surface glycoprotein
  • Specific‐willnotfusewithother
  epithelia e.g. tongue

Question 24

How does the mid-line disintegrate (3)?

Answer 24

1) Epithelial-Mesenchymal Transition
2) Apoptosis of epithelial cells
3) Migration to the nasal or oral edge

Question 25

what happens when palatal shelves fail to fuse?

Answer 25

cleft palate

Question 26

what happens if there is epithelial remnants?

Answer 26

– Epithelial cell rests

– Cystic potential

Question 27

Discuss fusion problems.

Answer 27

• Palatal clefts are one of most common congenital abnormalities (1:2500 live births)
• Most frequent in females- due to process starting one week later(?)
• Recent data multifactorial (67% of all cleft lip; 41% cleft palate and 34% sub- mucosa)
• Only 20% cleft palates monogenic, 5% caused by teratogens, 1% chromosomal abnormalities, 20% of unknown aetiology.
• Risk factors- Smoking, alcohol abuse, drugs-both medical and recreational, viruses, rubella. To much Vitamin A (or other retinoids) and deficiencies in folic acid.

Question 28

what is HA made by?

Answer 28

3 different enzymes:

• HA synthase 1
• HA synthase 2
• HA synthase 3

Question 29

where are these enzymes found?

Answer 29

Found on different chromosomes and are expressed different times during development