- Specialised connective tissue
- Function: Supportive in nature
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- Glycosaminoglycans (as proteoglycans)
- Chondroitin sulphate
- Keratan sulphate
- Hyaluronic acid
- Glycoproteins
- Chondronectin
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- Mesenchymal cells aggregate, round up and become chondroblasts
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- Chondroblasts secrete matrix and fibres
- Each chondroblast becomes surrounded by the fibres and matrix that it produces
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- They eventually occupy spaces called lacunae
- Chondroblasts finally mature into chondrocytes
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Interstitial Growth:
- Internal cartilage growth by activity of chondrocytes within their lacunae
- Individual cartilage cells divide and lay down matrix
- Young cartilage grows like this
- Addition of new cartilage from the periphery by activity of chondroblasts in the perichondrium
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- Only the perichondrium receives blood supply
- The chondrocytes are nourished by diffusion through the matrix
- (This differentiates it from bone where diffusion is prevented by the calcified matrix)
- The matrix is hydrated to facilitate this diffusion
- In articular cartilage where there is no perichondrium nourishment is from the synovial fluid
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- Hyaline
- Elastic
- Fibrous
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- “Hyaline” is derived from the greek word “hyalos” meaning glass because of its characteristic translucent appearance
- Covered with perichondrium
- ( EXCEPTION: Articular cartilage)
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- Growth of the cartilage is both appositional from the perichondrium and interstitial
- A characteristic feature is the occurrence of isogenous groups or cell nests
- Cells lie in lacunae
- Young cells are peripheral, flattened or elliptical with their long axis parallel to the surface
- Towards the interior they become oval or hypertrophied
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- Once a cell divides, matrix is secreted to separate the daughter cells so that they lie in separate lacunae
- These divide to result in a group of chondrocytes in neighbouring lacunae
- Each cluster is said to be isogenous because it represents the progeny of a single chondrocyte
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- Secreted by the chondrocytes
- Semi-translucent blue-gray coloured
- Homogeneous- the fibres in it have approximately the same refractive index as the ground substance
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- 40% of the weight of the cartilage is collagen
- Type II collagen is the predominant type
- Types VI, IX, X and XI are minor collagens (5-10% of the collagen)
- Capsular matrix (C): intensely basophilic thin rim around the isogenous groups. Minor collagens lie here and provide structural support
- Territorial matrix (TM): Basophilic region around this due to increased levels of chondroitin sulphate
- Inter-territorial matrix (IT): Less basophilic regions between cell groups
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- With age hyaline loses its translucency and becomes less cellular
- Less basophilia due to loss of proteoglycans
- The most important age change is calcification
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- Found in
- Auricle
- External auditory canal
- Eustachian tube
- Epiglottis
- Smaller laryngeal cartilages
- Elastic fibres in the matrix give it a yellowish appearance (yellow elastic tissue)
- Auricle
- External auditory canal
- Eustachian tube
- Epiglottis and smaller laryngeal
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- Covered with perichondrium- similar structure to hyaline cartilage
- Growth occurs by interstitial and appositional types
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- Chondrocytes have similar structure but are not found in isogenous groups
- Occur singly or in pairs separated by the matrix that the cells secrete
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- Contains type II collagen and elastic fibres (non-homogeneous matrix)
- Thus more flexible than hyaline
- Less likely to undergo calcification
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- Found in:
- Intervertebral discs of the vertebral column
- Pubic Symphysis
- Intra-articular discs (menisci)
- Glenoidal and acetabular labrum
- Found where tough support or tensile strength is required
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- Resembles dense regular connective tissue
- Not really like modified hyaline cartilage
- More like a transition between cartilage and tendons/ ligaments
- Develops similar to ordinary connective tissue
- Fibroblasts are converted to chondrocytes which lay down matrix
- The fibres are principally type I collagen
- Hence the matrix is mainly acidophilic
- Chondrocytes are imprisoned in lacunae which occur in rows between the thick collagen bundles
- There is no perichondrium
- Growth is purely interstitial
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