Cartilage

Cartilage

1. Composition

   • cellular
     • chondrocytes
       • cells remain close together
         • groups of 2-4 cells called a nest
           • matrix enclosed compartments that the cells sit in are called lacunae
       • secretory cells with a basophilic cytoplasm (due to loads of RER)
       • other chondrocytes contain fat droplets
       • cluster of chondrocytes is known as an isogenous group and it is enclosed by territorial matrix
     • chondroblasts
       • found in the outer layer of cartilage
       • as they secrete matrix and fibres, they become trapped inside and mature into chondrocytes
       • contain lipids and glycogen

2. Perichondrium

   • surrounds the surface of hyaline cartilage
   • continuous with the periosteal cover of bone
   • outer fibrous layer of fibroblasts
     • produce collagen
   • inner chondrogenic layer of chondroblasts
   • vascularised

3. Function

   • support soft tissue
   • provides a smooth gliding surface for bone articulations at joints
   • enables development and growth of long bones (endochondral ossification)

4. Types of cartilage

   • hyaline
     • most common type of cartilage
     • matrix contains a moderate amount of collagen fibres
     • avascular
     • surrounded by perichondrium
     • type 2 collagen interacts with proteoglycans
     • occurs in articular cartilage, costal cartilage, cartilage of the respiratory tract and cartilage of embryos
       • articular cartilage contains no nerves
       • layers of articular cartilage
         • surface layer
           • STZ
             • middle zone
               • deep zone
                 • calcified zone
                   • subchondral zone
   • fibrocartilage
     • matrix contains a limited number of cells and ground substances
     • substantial amount of collagen fibres
     • generally avascular
     • lacks perichondrium
     • consists of chondrocytes and fibroblasts surrounded by type 1 collagen
     • between hyaline cartilage and dense connective tissue
     • chondrocytes aligned along lines of stress
     • found in intervertebral discs, articular discs of the knee, mandible, pubic symphysis and sternoclavicular joints
   • elastic
     • matrix contains collagen fibres
     • large number of elastic fibres
     • avascular
     • surrounded by perichondrium
     • type 2 collagen interacting with proteoglycans and elastic fibres
     • external ear, epiglottis and auditory tube

5. Growth

   • chondrogenesis
   • insterstitial growth
     • chondrocytes grow, divide and lay down more matrix inside the existing cartilage
   • appositional growth
     • new cartilage is added to the surface of cartilage by chondroblasts from the inner layer of the perichondrium

6. Degradation

   • collagenases
   • gelatinases
   • aggrecanases
   • stromelysins
   • cytokines (IL-1 and TNF)
   • NSAIDs and less glucocorticoids

7. Synthesis

   • collagens, proteoglycans, proteins, more growth factors (IGF-1 and TGFbeta), less cytokines and less NSAIDs

8. Healing

   • superficial cartilage injuries will not heal
     • if the injury penetrates the subchondral bone then the cartilage will heal
       • heals with fibrocartilage due to the network of vessels in subchondral bone

9. Injuries

   • acute
     • due to trauma
   • chronic
     • due to previous injuries or disease

Imagens e arquivos do mapa