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CFD > CDF8- the development of the mandible and tongue > Flashcards

CDF8- the development of the mandible and tongue Flashcards

1
Q

what is the mandibular process?

A
  • developmental structure

- lower 1/3 of face in early development -gives rise to mandible chin, lower lip etc

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2
Q

what is the mandible?

A
  • a bone

- the lower jaw

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3
Q

what pharyngeal arch gives rise to the mandible?

A

1

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4
Q

what is cartilage?

A

Type of connective tissue that is strong, flexible and semi rigid supporting tissue

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5
Q

what can the cartilage withstand?

A

compression forces and yet it can bend

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6
Q

what is cartilage made by?

A

chondroblasts and chondrocytes

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7
Q

what is the ECM composed of?

A

10% Aggrecan, 75% water and a mix of collagen fibres

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8
Q

what are the 3 types of cartilage?

A

Hyaline
fibrocartilage
Elastic cartilage

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9
Q

what appearance does hyaline have?

A

glassy appearance

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10
Q

Describe fibrocartilage.

A

tendon insertions and

intervertebral discs: reinforced with collagen bundles

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11
Q

what is made of elastic cartilage and what are it properties?

A

-external ear and
epiglottis
-flexible and resilient- has elastic fibres

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12
Q

what is cartilage for?

A

1) To form the supporting framework of some organs, such as the walls of airways (nose, trachea, larynx and bronchi), where it prevents collapse
2) To form the articulating surface of bones

3) To form the template for the growth and development of
long bones and most of the rest of the foetal skeleton (where gradually replaced by bone)

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13
Q

Discuss cells of cartilage -chondroblast and chondrocyte.

A

ECM secreted by chondroblasts, found in covering layer of cartilage.
Once trapped inside mature into chondrocytes- can divide to form nests of 2-4 cells.
Matrix enclosed compartments called lacunae. Chondrocytes large secretory cells with lots of Rough ER

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14
Q

what is the surface of most cartilage?

A

dense irregular connective tissue called perichondrium

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15
Q

what is the outer layer and inner layer of cartilage?

A

outer layer- contains lots of collagen producing fibroblasts

inner layer -contains chondroblasts

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16
Q

why is cartilage unlike other connective tissue?

A

avascular

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17
Q

what are the 2 mechanisms of growth of cartilage and describe them?

A

a) Interstitial growth- chondrocytes grow and divide lay down more matrix
inside the existing cartilage-developmental
b) Appositional growth- new surface layers of matrix are added to the pre-
existing matrix by new chondroblasts from the perichondrium

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18
Q

what is meckel’s cartilage?

A

Cartilage of 1st Arch
The mandible itself is preceded by Meckel’s cartilage.
Rod of cartilage around 6th week IUL

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19
Q

where does meckel’s cartilage extend from?

A

the otic capsule (bony capsule of developing inner ear) to a midline symphysis

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20
Q

when is the mandible formed?

A

By week 10

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21
Q

what involvement does meckels cartilage have on the formation of the mandible?

A

has very little direct involvement-

probably bone follows line of cartilage (uses as a template)

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22
Q

what becomes of the posterior extremity of the cartilage?

A

forms malleus of inner ear and the sphenomalleolar ligament

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23
Q

what happens to the cartilage from the sphenoid to the division of mandibular nerve ? what is left over?

A
  • cartilage totally disappears

- its fibrocellular capsule persists as the sphenomandibular ligament

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24
Q

what happens to the cartilage from the lingual forward to the division of alveolar nerve into the incisive and mental branches?

A

fully absorbed

25
Q

what does the cartilage towards to midline make a contribution to?

A

contribution to mandible by endochondral ossification

26
Q

what is the role of growth factors in meckels cartilage development?

A

1) CCN2 (or Connective tissue growth factor)-required for the proper development of orofacial region.
2) CCN2 null mice cleft palate.

3)Significant contribution to mandibular morphogenesis and tooth development.
In Mandibular development: 2 stages in MC primordium strong CCN2 gene expression.
CCN2 accelerates adhesion and aggregation of 1st arch cells. As grows CCN2 expression silenced then hypertrophic chondrocytes express and recruit osteoblasts.

4) Critical promoter of physiological and Pathological remodelling
5) Periodontal fibrosis from smoking soon to be used as therapeutic factor in periodontal fibrosis

27
Q

Describe the ossification involved in the formation of mandible.

A

1) Forms at start by intramembranous ossification-primary ossification centre between the incisive and mental nerve.
2) Growth factors involved in this are Vascular Endothelial Growth Factor (VEGF). Transforming growth factor beta-1 and probably some of the BMPs.
3) However, the ossification changes to endochondral ossification at the secondary cartilage sites

28
Q

what are the 2 stages of the ossification pathway?

A

a) intramembranous

b) endochondral

29
Q

Describe the ossification pathway.

A

a) Intramembranous ossification process starts with osteoblast differentiation from within mesenchymal condensation
(b) Endochondral ossification starts with the formation of condensed mesenchyme, in which chondrocytes develop forming a cartilaginous element prefiguring the future skeletal element

30
Q

what is osteogenesis ?

A

the process of laying down new bone material by osteoblasts

31
Q

when does initial formation of mandible begin?

A

6 weeks I.u.l

32
Q

how does the mandible first appear?

A

a band of dense fibrocellular tissue

33
Q

where does intramembranous ossification start (week 7 i.u.l)?

A

lateral to incisive / inferior alveolar nerve

34
Q

where does the formation of bone spread?

A

spreads rapidly backward below the mental nerve and on the lateral side of inferior alveolar nerve (enveloping incisive /inferior alveolar nerve/mental nerves)

35
Q

what happens to merkels cartilage when bone forms?

A

it disappears

36
Q

Name the 3 mandibular secondary cartilages.

A
  • coronoid
  • condylar
  • symphyseal
37
Q

when does the condylar cartilage appear and disappear?

A

-appears 10-12 weeks IUL -Disappear 20 years of age

38
Q

when does the coronoid cartilage appear and disappear?

A

-appear 14-16 weeks IUL -disappear before birth

39
Q

when does the symphyseal cartilage appear and disappear?

A
  • appear 16 weeks

- disappear 1st year after birth

40
Q

how is secondary (growth) cartilages different from primary cartilage?

A
  • not part of primary (cartilaginous) skeleton
  • fibrocartilage (not hyaline cartilage)
  • appositional growth rather than interstitial growth
  • Produce (type of ) Endochondral Ossification (Greek- endon within chondros-cartilage)
41
Q

Describe secondary (growth) cartilages : endochondral ossification.

A
  • Surface deposition of new cartilage
  • Calcification of sub-surface cartilage
  • Resorption of calcified tissue
  • Replacement of calcified cartilage with bone
42
Q

Name some developmental abnormalities of the mandible.

A

1) Agnathia (no mandible)
- lack of ectomesenchyme in mandibular arch
- fatal
2) Micrognathia (very small mandible)
- lack of ectomesenchyme in arch
- occurs in certain syndromes including Downs
3) Macrognathia (very large mandible) -genetic
- usually seen with pituitary disorder (eg Acromegaly)

43
Q

what does the 3rd pharyngeal arch form?

A

◦ greater horn of hyoid
◦ inferior hyoid body
- root of the tongue
-stylopharyngeal muscle

44
Q

when does development of the tongue start?

A

4 weeks i.u.l

45
Q

what is involved in the development of the tongue?

A 
-1st pharyngeal arch :
2 lingual swellings (laterally)
1 tubercular impar 
-3rd pharyngeal arch:
hypobranchial eminence 
-4th pharyngeal arches
-Occipital somites
46
Q

what forms the muscles in the tongue?

A
  • 4th pharyngeal arch - palatoglossus

- occipital somites- all other (intrinsic and extrinsic)

47
Q

what happens to the 2 lingual swellings and 1 tubercular swelling?

A

turns into 1 big swelling

48
Q

what part of the tongue does the 1st arch form?

A

anterior 2/3

49
Q

what part of the tongue does the 3rd arch form?

A

posterior 1/3

50
Q

what part of the tongue does the 4th arch form?

A

glottis and epiglottis

51
Q

Describe the detachment of anterior 2/3 of the tongue.

A

-Ectoderm grows between anterior 2/3 and underlying arch
-Ectoderm degenerates except in the midline :
separation of tongue
except for midline frenulum

52
Q

what is the origin of lingual mucosa of the anterior 2/3rds ?

A
  • 1st pharyngeal arch
  • general sensory innervation: Trigeminal V
  • taste innervation: chorda tympani -facial nerve VII
53
Q

what is the origin of the palatoglossus?

A
  • 4th pharygeal arch

- innervation via pharyngeal plexus ; vagus X/accessory

54
Q

what is the origin of all other muscles (intrinsic and extrinsic)?

A
  • migration from occipital somites

- innervation:hypoglossal nerve XII

55
Q

Name some developmental abnormalities of the tongue.

A

-Failure of fusion (forked tongue)
-Imperfect detachment (Ankyloglossia)
-Growth disorders:
Aglossia (rare)
Microglossia
Macroglossia

56
Q

what does the 2nd arch form?

A 
◦ Stapes
◦ Lesser horn and superior hyoid body
◦ styloid process, stylohyoid ligament
-muscles:facial expression and PBD
-thyroid gland and tonsil 
-nerve :VII facial
57
Q

Describe the stages of the development of the thyroid gland.

A
  • associated with tongue development
  • Epithelial down-growth from foramen caecum
  • migration down midline to level of thyroid cartilage (thyroglossal duct)
  • formation/proliferation of thyroid tissue
  • disintegration of thyroglossal duct
58
Q

Name some abnormalities of thyroid development.

A

-Ectopic thyroid gland :tissue left behind during development e.g. lingual thyroid gland
-persistent thyroglossal duct
-pathological changes to remnants of thyroglossal duct:
thyroglossal cyst
thyroglossal fistula

CFD (10 decks)

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