cartilage l General Histology & biology revision for dental students

 

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Cartilage

Definition  :

• special type of Connective tissue with firm consistency rigid , weight bearing with some flexibility
• It’s type of mesenchymal tissue , poor in blood supply & has firm or rubbery matrix which is basophilic

►Types:                            

1. Hyaline cartilage        
2. Yellow elastic fibro-cartilage    
3. White fibro-cartilage 

►Site:                               

1. Costal cartilage of thoracic cage
2. Articular surface of bone Trachea bronchi & nose is main of fetal skeleton
3. Laryngeal cartilage (thyroid / cricoid)

 

hyaline carilage

•  the commonest type of cartilage
•  Appearance transparent pale blue (hyaline = glassy )
•  Consistency: firm with some flexibility 

  Structure:            

1. Perichondrium             
2. cartilage cells =chondrocyte               
3. matrix

1-Perichondrium

Definition:

• vascular CT which surrounds the cartilage except at the articular surfaces of the joints Two layers 
• Outer fibrous layer:

1. Formed of fibrous connective tissue      
2. rich in collagen type II, fibroblasts and blood vessels

• Inner chondrogenic layer: 

1. formed of cartilage forming cells (chondroblast)
2. divide and differentiate into chondrocytes which secrete the cartilage matrix

2-cartilage cells =chondrocyte

Young chondrocytes

• arise from inner chondrogenic layer

• site :

1. periphery of the cartilage
2. parallel to the perichondrum

• Light microscope :

1. Shape : flat cells
2. nuclei : open-face
3. cytoplasm : pale basophilic
4. number in lacuna
5. present singly in their lacunae

Old ( mature) chondrocytes

• arise from Young chondrocytes

site :

1. deep in the cartilage
2. perpendicular to perichondrumLM

Shape :

•   oval or rounded “when single’ Triangular or
•   semicircular (when in groups)

Light microscope :

1. nuclei :  rounded &open face
2. number in lacuna : present in groups in single lacuna called cell nest
3. can divide   &  show multiple mitotic figures

Electron microscope :

• Rough endoplasmic reticulum , ribosomes & well developed Golgi

3- matrix

characters :                       

• rubbery in consistency       
• non vascular
• homogenous although containing collagen fiber ( as collagen fiber  has the same refractive index of the amorphous substance )

Components :                   

• Collagenous fiber which is invisible
• amorphous substance :     

1. proteoglycan linked with chondroitin sulphuric acid
2. chondrocalcin : help calcification

Function :

• Allow diffusion O2 + Nutrients to cartilage cells

2- Yellow elastic fibro-cartilage

Structure : Identical to hyaline cartilage except that

• matrix is non homogenous & flexible as it is very rich in elastic  fiber

Sites  

1. Ear Auricle
2. External auditory meatus
3. Epiglottis
4. Eustachian tube.

3- White fibro-cartilage

Structure : Differ from hyaline cartilage in

1. white colour in fresh state
2. tens and resists stretch due to presence of  collagen fibers
3. perichondrium not covered by perichondrium but it is surrounded by dense C, T. rich in blood vessels from which it is nourished
4. Chondrocytes: Either arranged in rows or  columns.Either present singly or in groups inside their lacunae
5. Matrix: Collagen fibers are in bundles between the rows of chondrocytes bundles arrangement.