CFD 7 - face, jaws and mouth 2 Flashcards
What branchial arch forms the mandible?
1st arch
What branchial arches form the tongue?
1st, 3rd and a bit of 4th arches
What branchial arch forms the thyroid gland?
2nd arch
What is cartilage?
- very specialised connective tissues
strong, flexible and semi rigid supporting tissue - can withstand compression forces and yet it can bed
How is cartilage made, and what is it made of?
- made by chondroblasts and chondrocytes
- ECM rich, 10% Aggrecan, 75% water and a mix of collagen fibres
What are the 3 types of cartilage?
- hyaline (most common)
- fibrocartilage
- elastic cartilage
Where is hyaline cartilage present?
- nose
- tracheal rings
- larynx
- articular rings
- bronchi
- ventral ends of the ribs
- articulating surfaces of the long bones
(most common type)
What is the key feature of elastic cartilage?
abundant elastic fibres in its matrix
Where does elastic cartilage function?
- epiglottis
- cruciform cartilage of the larynx
- auditory canal and tube
What is the key feature of fibrocartilage?
contains bundles of collagen fibres associated with either hyaline cartilage or dense regular connective tissue
Where can fibrocartilage be found?
- vertebral discs and intervertebral areas
- insertion of some tendons
- in the pubic symphysis
What appearance does hyaline cartilage have?
glassy appearance
What are the most important things to know about fibrocartilage?
- tendon insertions and intervertebral discs
- reinforced with collagen bundles
What are the most important things to know about elastic cartilage?
- external ear and epiglottis
- flexible and resilient - has elastic fibres
What are the 3 main functions of cartilage?
- to form the supporting framework of some organs, such as the walls of the airways, where it prevents collapse
- to form the articulating surfaces of bones
- to form the template for the growth and development of long bones and most of the rest of the foetal skeleton (where gradually replaces by bone)
What are the cells of cartilage?
chondroblasts and chondrocytes
What are chondroblasts?
- generally a fairly primitivee mesenchymal cell
- usually found in the covering layer of cartilage
- secrete ECM
What happens do chrondoblasts once they’ve laid down cartilage?
tend to get trapped inside and they mature into chondrocytes
What do chondrocytes form?
can divide to form nests of 2-4 cells
Where is the matrix of the cartilage laid down?
in enclosed compartments called lacunae
What are chondrocytes?
large secretory cells with lots of rough ER, that lay down a very specific matrix
What is the surface of most cartilage?
dense irregular connective tissue called perichondrium
What does the outer layer of cartilage contain?
lots of collagen producing fibroblasts
What does the inner layer of cartilage contain?
chondroblasts
Why is cartilage unlike other connective tissue?
is it avascular
What are the 2 growth mechanisms for cartilage?
- interstitial growth
- appositional growth
What is interstitial growth?
chrondrocytes grow and divide, lay down more matrix inside the existing cartilage - developmental
What is 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?
the main cartilage of the 1st arch, forms the mandible
What does Meckel’s cartilage contain lots of?
collagen and aggrecan (a glycosaminoglycan)
What does Meckel’s cartilage do?
- Meckel’s cartilage next to formation of new bone
- bone is being laid down next to the cartilage
- the cartilage is acting as a template for the bone formation
- once bone is laid down, cartilage is reabsorbed and becomes other things
What does Meckel’s cartilage precede?
the mandible
Where does Meckel’s cartilage extend from and to?
from the otic capsule (bony capsule of developing inner ear) to a midline symphysis
What are the 4 divisons of Meckel’s cartilage?
- posterior extremity
- from the sphenoid to the division of mandibular nerve
- from the lingual nerve forward to the division of the alveolar nerve into the incisive and mental branches
- forward to the midline
What is the fate of the posterior extremity (1) of Meckel’s cartilage?
forms malleus of inner ear and the sphenomalleolar ligament
What is the fate of the second division of Meckel’s cartilage (2)?
cartilage totally disappears - but its fibrocellular capsule persists as the sphenomandibular ligament
What is the fate of the 3rd division of Meckel’s cartilage (3)?
totally absorbed
What is the fate of the 4th division of Meckel’s cartilage (4)?
makes a contribution to mandible by endochondral ossification
What growth factor has a role in Meckel’s cartilage development?
CCNS (connective tissue growth factor)
What is the importance of CCN2?
- required for the proper development of orofacial region
- significant contribution to mandibular morphogenesis and tooth development
- later in life, a critical promoter of physiological and pathological tissue remodelling
In addition to its involvement in fibrotic disorders in a variety of organs, what has CCN2 been reported as a mediator of?
periodontal fibrosis caused by several factors including smoking
What is the regulation of gene expression and molecular function of CCN2 a possible therapeutic strategy against?
periodontal disease
During mandibular development, what are the 2 distinct stages that CCN2 gene expression is observed to occur in?
- at the first stage, strong CCN2 expression is detected throughout the Meckel’s cartilage primordium before the cartilaginous structure becomes evident, suggesting the contribution of CCN2 to Meckel’s cartilage formation itself
- after the initial formation of Meckel’s cartilage CCN2 production is then silences in the chondrocytes, then it recurs during hypertrophic like differentiation of the cells
What does CCN2 accelerate the adhesion and aggregation of?
the 1st branchial arch cells
What is the fundamental role of CCN2?
The fundamental role of CCN2 is as a messenger from chondrocytes to osteoblasts to guide the ossification
What kind of ossification is involved in the formation of the mandible?
Starts as intra-membranous ossification but as we get towards final development some of the ossification will change to endochondral at the secondary cartilage sites
What growth factors are involved in ossification of the mandible?
- Vascular Endothelial Growth Factor (VEGF)
- Transforming growth factor beta-1
- probably some of the BMPs
How does formation(ossification) of the mandible begin?
- primary ossification centre (between incisive and mental nerve)
- begins with a condensation to form the first bone of the mandible
- formation of bones spread rapidly anteriorly towards midline and posteriorly towards the point where the mandibular nerve divides into the lingual and the inferior alveolar nerve branches
Where does bone formation spread after spreading the the division of the IAN?
- spreads backwards and down, envelopes the incisive, mental and inf. alveolar nerves
- continues to spread anteriorly
Where do the lateral and medial plates of the mandible unite once they have grown?
beneath the incisive nerve
What does the backwards extension of ossification along the lateral aspect of Meckel’s cartilage form?
- a ‘gutter’ which will layer be covered and contains the inferior alveolar nerve
- this backwards ossification proceeds in the condensed mesenchyme to the point where the mandibular nerve separates at the midline to the lateral and alveolar plates
After completing the backwards ossification, where does the mandible then grow?
It will then develop upwards until where the bone will develop tooth germs, where they can form and occupy a second through of bone - area of tooth germs surrounded by bone
How does the ramus of the mandible develop?
develops by the rapid spread of ossification posteriorly into the mesenchyme of the first arch and it’s going to turn away from Meckel’s cartilage and will start to grow upwards, a divergence along the line of the mandibular nerve
What are the 3 mandibular secondary cartilages?
- condylar
- coronoid
- symphyseal
When does the condylar secondary cartilage appear and disappear?
- appears 10-12 weeks IUL
- disappears 20 years of age
When does the coronoid secondary cartilage appear and disappear?
- appears 14-16 weeks IUL
- disappears before birth
When does the symphyseal secondary cartilage appear and disappear?
- appears 16 weeks IUL
- disappears 1st year after birth
What is the cellular difference between secondary cartilage and primary cartilage?
secondary cartilage has a different historical structure to primary cartilage - cells are larger, less intracellular matrix
What does the condylar cartilage do?
- forms a cone shaped mass that occupies most of the developing ramus
- the mass of this is quickly covered and converted to bone by endochondral ossification
- after 20 weeks only a thin later remains, and persists until ~20yo, provides a mechanism for growth of mandible
What does the coronoid cartilage do?
- surmounts the anterior border on the top of the coronoid process
- relatively transient
- disappears long before birth
What does the symphyseal cartilage do?
appears in the connective tissue between the two ends of Meckel’s cartilage, but are entirely independent of it. Obliterated in the 1st year after birth
In what way does secondary cartilages differ from primary cartilage?
- cells are larger, less intracellular matrix
- not part of primary (cartilaginous) skeleton
- fibrocartilage (not hyaline cartilage)
- appositional growth rather than interstitial growth
What type of ossification do secondary cartilages produce?
(type of) endochondral ossification
What is involved in the endochondral ossification by the secondary cartilages?
- surface deposition of new cartilage
- calcification of sub-surface cartilage
- resorption of calcified tissue
- replacement of calcified cartilage with bone
