CFD7 - Palatogenesis: the formation of the palate Flashcards Preview

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1

when is the palate formed?

weeks 6-12

2

when palate forms, what is initially common?

oro-nasal cavity

3

what does the primary palate demarcates?

oral vs nasal components

4

what is the primary palate derived from?

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

5

what occurs at the 8th week?

Ossification centres palate around the perpendicular plate

6

what type of ossification is it?

intramembranous ossification

7

what is intramembranous ossification?

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

8

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

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

9

what does mesenchyme do?

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

10

what direction does the palatal shelves grow and why ?

-Grows down the sides
- tongue occupies a large proportion of the ora-nasal cavity

11

Does the mesenchyme attach to the side of the tongue?

NO-
glycoproteins on the tongue do not allow these structures to fuse

12

why are lateral palatal shelves vertically orientated?

insufficient space due to large tongue

13

what happens when the tongue withdraws downwards?

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)

14

what happens to form secondary palate?

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

15

Give overview of palatal shelf elevation.

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

16

what causes palatal elevation?

Forces extrinsic to the palate (Involving the tongue)
 Intrinsic forces generated within the palate

17

Describe the extrinsic factors.

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

18

Describe the intrinsic factors.

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

19

when does amount of water that the GAG binds increase?

during palatal shelf elevation

20

what are other theories for palatal shelve elevation?

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

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

21

How does the palatal shelves fuse?

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

22

what type of fusion is it when palatal shelves fuse?

true fusion

23

Describe epithelial adhesion .

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

24

How does the mid-line disintegrate (3)?

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

25

what happens when palatal shelves fail to fuse?

cleft palate

26

what happens if there is epithelial remnants?

– Epithelial cell rests
– Cystic potential

27

Discuss fusion problems.

-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.

28

what is HA made by?

3 different enzymes:
- HA synthase 1
-HA synthase 2
-HA synthase 3

29

where are these enzymes found?

Found on different chromosomes and are expressed different times during development