Flashcards in CDF8- the development of the mandible and tongue Deck (58)
what is the mandibular process?
- developmental structure
-lower 1/3 of face in early development -gives rise to mandible chin, lower lip etc
what is the mandible?
-the lower jaw
what pharyngeal arch gives rise to the mandible?
what is cartilage?
Type of connective tissue that is strong, flexible and semi rigid supporting tissue
what can the cartilage withstand?
compression forces and yet it can bend
what is cartilage made by?
chondroblasts and chondrocytes
what is the ECM composed of?
10% Aggrecan, 75% water and a mix of collagen fibres
what are the 3 types of cartilage?
what appearance does hyaline have?
tendon insertions and
intervertebral discs: reinforced with collagen bundles
what is made of elastic cartilage and what are it properties?
-external ear and
-flexible and resilient- has elastic fibres
what is cartilage for?
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)
Discuss cells of cartilage -chondroblast and chondrocyte.
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
what is the surface of most cartilage?
dense irregular connective tissue called perichondrium
what is the outer layer and inner layer of cartilage?
outer layer- contains lots of collagen producing fibroblasts
inner layer -contains chondroblasts
why is cartilage unlike other connective tissue?
what are the 2 mechanisms of growth of cartilage and describe them?
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
what is meckel's cartilage?
Cartilage of 1st Arch
The mandible itself is preceded by Meckel’s cartilage.
Rod of cartilage around 6th week IUL
where does meckel's cartilage extend from?
the otic capsule (bony capsule of developing inner ear) to a midline symphysis
when is the mandible formed?
By week 10
what involvement does meckels cartilage have on the formation of the mandible?
has very little direct involvement-
probably bone follows line of cartilage (uses as a template)
what becomes of the posterior extremity of the cartilage?
forms malleus of inner ear and the sphenomalleolar ligament
what happens to the cartilage from the sphenoid to the division of mandibular nerve ? what is left over?
-cartilage totally disappears
- its fibrocellular capsule persists as the sphenomandibular ligament
what happens to the cartilage from the lingual forward to the division of alveolar nerve into the incisive and mental branches?
what does the cartilage towards to midline make a contribution to?
contribution to mandible by endochondral ossification
what is the role of growth factors in meckels cartilage development?
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
Describe the ossification involved in the formation of mandible.
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
what are the 2 stages of the ossification pathway?
Describe the ossification pathway.
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