CARTILAGE AND BONE




HARD TISSUE: cartilage, bone (osseous tissue)

    skeletal framework

    evolutionary (phylogenetic) concept:

      exoskeleton ------ protection, maintenance of form, but movement limitaion

      endoskeleton: chordates ------- free and fast movement

        cartilage; cartilagenous fish

        bone; from bony fish

    ontogeny:

      cartilage ----------------------------- bone

      in adult - few

      1. flexible tube

        wall of the major respiratory passage

          larynx; epiglottis,part of corniculate and cuneiform cartilage

          trachea, bronchus

        auditory tube: external auditory meatus, Eustachian tube, auricle

      2. end of bones or between bones

        costal cartilage

        diarthrosis: articular cartilage

        symphysis; intervertebral disk, symphysis pubis

      - sometimes degenerates and transforms to bony tissue


    Cartilage vs. Bone

    - Similarities

      1. hard tissue

      2. lacuna-matrix system

        matrix: collagen, proteoglycan

      3. osteoblast-osteocyte, chondroblast-chondrocyte

        secretes collagen, proteoglycan

      4. surrounded by perichondrium or periosteum

    - Differences: Bone is deposited by inorganic matrix


    Cartilage

    Bone

    components

    no inorganic substance

    organic substance

    flexibility

    high tensile strength
    resilence, elasticity

    harder
    no flexibility

    nutrition and
    blood vessel

    diffusion
    avascular

    canaliculi-Haversian system
    vascular

    mechanism of
    growth and
    remodelling

    interstitial and
    appositional growth,
    no remodelling

    appositional growth only,
    destruction by osteoclast,
    constantly remodels





CARTILAGE

    1. Cellular Element

      Chondroblast - Chondrocyte

        cf. fibroblast - fibrocyte, osteoblast - osteoclast

      a. cells synthesize protein

      b. lost activities and become chondrocyte

      c. dependent on hormonal and nutritional factors

        growth Hormone

        steroid hormone

        vitamin C

      - secretes collagen (type II), proteoglycan

        euchromatic, prominent nucleolus

        abundant r-ER, Golgi in chondroblast

        glycogen deosition increase in chondrocyte

      - lacunar system

        shrinks during fixation and staining

        fill the lacuna completely in normal condition

      - isogenous cell group

        interstitial growth

    2. Matrix (Ground Substance)

      (1) Mucopolysaccharides: Aggrecan polymer

          Proteoglycans: Chondroitin-4-sulfate, Chondroitin-6-Sulfate, Keratan Sulfate -- basophilia

          Hyaluronic Acid, central core of aggrecan polymer

        - Possible Function:

          a. holding water

            75% of cartilage; fluid

            nutrition by diffusion

          b. holding collagen

            provides gel-like glue material

            act as a molecular sieve - limits mobility

        - Territorial (Capsular) Matrix - rich MPS, poor collagen

        - Interterritorial Matrix - rich collagen, poor MPS

      (2) Connective Tissue Fiber: Collagen, Elastin

        Type II Collagen ----- Hyaline Cartilage

        Elastin ----------------- Elastic Cartilage

        Type I Collagen ------ Fibrocartilage

      (3) chondronectin

        - promotes adherence of chondrocytes to matrix collagen


    3. Perichondrium

      - dense connective tissue surrounding cartilage

      - harbors vascular supply of the avascular cartilage

      - absent in

        a. articular cartilage

          diffusion of nutrient via synovial fluid

        b. fibrocartilage

    4. Type (Classification)

      1) Hyaline Cartilage

        cartilage prototype, most widely distributed type

        costal, articular and tracheobronchial cartilage

        collagen type II

        easily degenerates

          poor diffusion - hypertrophy - calcification - cell death

        cartilage in intracartilagenous bone formation


      (2) Elastic Cartilage

        epiglottis, part of corniculate and cuneiform cartilage

        collagen type II

        abundant network of fine elastin fibril

        less susceptible to degenerative change than hyaline c.


      (3) Fibrocartilage

        intervertebral disk, symphysis pubis

        always associates with dense connective tissue

          gradual transition between border area

        long column of isogenous cell group

        matrix

          abundant collagen fiber

          small amount of proteogycan -- acidophilia

        no identifiable perichondrium



 

BONE (OSSEOUS TISSUE)


 

Lecture Note by Won Taek Lee, M.D., Ph.D.