CARTILAGE

n      Is a specialised type of connective tissue.

n      Consists of cells and extracellular components.

n      Does not contain vessels or nerves.

n       Bears weight and provides rigidity.

n      Is surrounded by a layer of dense connective tissue, the perichondrium

Functions of Cartilage Tissue

n      Firm consistency of the extracellular matrix allows the tissue to bear mechanical stresses without permanent distortion

n      Supports soft tissues.

n      Shock-absorbing because it is resilient.

n      Smooth surface allows sliding .

n      Essential for growth, development of bone.

Characteristics

n      Chondrocytes

¨     Located in lacunae

n      Extensive extra-cellular matrix

¨     Fibers, Collagen, &elastic

¨     Ground substance

¨      Fibers bind together and give firm, flexible properties to tissue

Chondrocytes

n      Produce and maintain extra cellular  matrix.

n      Either single or in isogenous groups .

n      Fat droplets, glycogen granules are found in cytoplasm.

n      Active  ones are more basophilic.

Cartilage matrix

n      Extracellular Components:

Solid ,firm, pliable

No vascular network

Include;

Collagen

Proteoglycans

Multiadhesive Glycoproteins

Collagen

n      Major matrix protein

n      5 types

Type ll

Type Vl

Type lX

Type X

Type Xl

Aggrecans

n      large proteoglycan molecules

Protein core

Glycosaminoglycans (chondroitin 4-sulfate and chondroitin 6-sulfate) attached to protein cores

n      100 to 200 aggecan molecules linked  non-covalently to hyaluronic acid

n      Huge complexes (3 – 4 micons long).

n      Negative charges (proteoglycan) attract Na+.

n      Fills interstices between collagen fibers.

n      Electrostatic bonds with collagen.

Multiadhesive glycoproteins

n      Influence interaction between the chondrocytes and the matrix molecules

n      Markers of cartilage turnover and degeneration

n      Examples

¨     Anchorin CII

¨     Tenascin

¨     Fibronectin

Cartilage matrix

n      Contains high concentration of bound sulfate so stains with basic dyes.

n      Rich in water(70-80%)

Types of cartilage

n      Hyaline cartilage

n       Elastic cartilage

n       Fibrous cartilage

Hyaline Cartilage   (Gr.hyalos,Glassy)

n      Fundamental type and most common

n      Occurrence:

Ø                  Ribs (ventral ends)

Ø                  Long bones (articular surfaces)

Ø                  Nose, Larynx, Trachea, Bronchi

Ø                  External auditory meatus (part)

Ø                  Fetal skeleton (except membrane bones)

Macroscopic appearance of Hyaline cartilage

•           Plates, columns, irregular masses

•           Solid

•           Flexible, elastic

•           Translucent

•           Bluish to pearly (glassy)

•           Enclosed with fibrous envelope

•           Calcifies with age

Microscopic structure

Cells embedded in clear matrix

Perichondrium on surface

The cartilage cells are called chondrocytes and lie within little spaces, the lacunae .

Chondrocytes

n      Produce and maintain extra cellular  matrix.

n      Either single or in isogenous groups .

n      Active  ones are more basophilic ,indicative of protein synthesis and clear areas as a result of large golgi apparatus.

n       Fat droplets, glycogen granules are found in cytoplasm of inactive cells.

With TEM

n      The active chondrocytes display numerous profiles of rER, a large golgi apparatus, secretory granules, vesicles,intermediate filaments, microtubules, and actin microfilaments

Extra cellular matrix

n      Components of hyaline cartilage matrix are not uniformly distributed.

n      Thus basophilia and metachromasia seen provide information about  the distribution and relative conc. of sulfated proteoglycans.

n      Matrix does not stain homogenously.

Extra cellular matrix

n      Pericellular matrix, immediately surrounding the chondrocytes

n      The matrix near the isogenous groups of chondrocytes is termed territorial matrix or capsule. In H&E stained sections the territorial matrix is more basophilic, i.e. it stains darker.

n      The remainder of the matrix is called the interterritorial matrix.

Perichondrium

n      Dense CT that covers cartilage

n      Contains blood, nerve supply, lymphatics.

n      Source of new cartilage cells

n      Divided into two layers

Inner cellular

Outer fibrous

Articular Cartilage

Hyaline cartilage of  articular surfaces do not posses a perichondrium

Zones of articular cartilage

1. superficial / tangential Zone

2. Intermediate/ trasitional Zone

3. Deep/Radial Zone

4. Calcified Zone

Repair of hyaline cartilage

n      Can tolerate considerable amount of stress

n      Limited ability to repair Because of

1. Immobility of chondrocytes

2. Inability of chondrocytes to proliferate

3. Avascularity

4. When hyaline cartilage calcifies it is replaced by bone

See histological slides here

ELASTIC CARTILAGE

n      Similar to hyaline cartilage but has elastic fibers running in all directions in addition to collagen.

n      Resorcin fuchsin stain and orcein stain

n      Found in auricle of ear, walls of external auditory canals, eustachian tubes, epiglottis of larynx

n      Maintains shape, deforms but returns to shape; flexibility of organ; strengths and supports structures.

See histological slides here

Fibrocartilage

n      Hyaline cartilage with dense connective tissue.

n      Chondrocytes may lie singly or in pairs, but most often they form short rows between dense bundles of collagen fibres  in contrast to other cartilage types

n      No surrounding perichondrium.

n      Rounded nuclei belong to chondrocytes.

n      In fibrous areas some nuclei are flat, they are of fibroblasts.

n      Contain type I and type ii collagen.

•         Collagen type I is dominant in fibrous cartilage

•         is typically found in relation to joints (forming intra-articular lips, disks and menisci) intervertebral disks, symphysis pubis.

It is difficult to define the perichondrium because of the fibrous appearance of the cartilage and the gradual transition to surrounding tissue types.

See histological slides here

Growth of Cartilage

n      Growth is attributable to two processes:

¨     Interstitial growth

n      Mitotic division of preexisting chrondrocytes

n      Synthesis of matrix

n      Expands cartilage matrix from within

n      Occurs in epiphyseal plates, articular cartilage

¨     Appositional growth

n      Differentiation of perichondrial cells ®    chondroblasts

n      Synthesis of matrix

n      Increase in girth