Cartilage and Articular Joint Lubrication -Rega Flashcards
What are some differences in bone vs cartilage (collagen type, make up, O2 requirement, covering)
bone:
- Type I collagen
- osteocytes embedded in collagen/inorganic matrix
- moderate O2 requirement
- vascularized
- covered with periosteum
cartilage:
- type II collagen
- chondrocytes embedded in collagen/proteoglycan matrix
- low O2 requirement
- anti-vascular, anti-clotting
- covered in perichondrium
What are some functional properties of cartilage? What do these functional properties rely on?
- stiffness
- durability
- distribution of load
rely on the extracellular matrix!!!
What composes 60-80% of the wet weight of cartilage?
tissue fluid (water with dissolved gases, small proteins and metabolites)
-structural macromolecules (proteoglycans and glycoproteins) only make up 20-40% of the weight
What secretes the extracellular matrix (ground substance) of cartilage?
chondrocytes
What structure of cartilage allows for its resistance of compression?
the glucosamine side units of proteoglycan repel each other and attract water and contribute to the stiffness of the cartilage
What structures of the body are composed of fibrocartilage?
- Glenoid labrum
- Acetabular labrum
- Articular discs (ie clavical)
- Lining of groove for tendons (ie biceps, etc.)
- Medial and lateral knee menesci
- Annulus fibrosis of IVD
What addition to the matrix in Elastic cartilage gives it an increased resistance? What is made of elastic cartilage?
elastin gives it resistance
- external ear
- corniculate cartilages of the hyoid
- epiglottis
- apices of arytenoids
What body parts are made of hyaline cartilage?
- costal
- nasal
- tracheal and bronchial and most laryngeal
- articular cartilage
- temporary
*What are some characteristics of articular cartilage?
-NO perichondrium
- 4 regions, orientation of collagen fibrils (from joint space–> bone):
1. tangential, parallel to the surface
2. intermediate=45 degrees to surface
3. radial, radial arrangement
4. calcified
*What are the differences in the zones of articular cartilage?
- tangential, parallel to the surface: resist high tensile load, fine densely packed collagen fibers, secrete proteins involved in surface lubrication
- intermediate=45 degrees to surface, right angles to each other: contains large amounts of water, MOST deformation under load
- radial, radial arrangement: fibers continue into calcified zone, many insert on subchondral bone for anchor
- calcified: matrix with calcium salts, anchors cartilage to bone, 3 and 4 separated by “tidemark” and increase age causes tidemark toward the surface
What region of articular cartilage contains the most water? What region undergoes the most deformation under load?
both are region 2==> intermediate region
What region of articular cartilage resists tensile/shear forces the best? Why?
Zone 1–> tangential
because it has the most densely packed collagen fibers
How/where will failure of collagen occur?
- failure: cracks propagate perpendicular to load
- maximum deformation and failure typically start in the tangential zone
What are the functions of articular cartilage?
- Distribute skeletal load
- Provide a friction-reducing, weight-bearing surface.
- Lubricate joint surface
- Absorb impact and minimize peak stresses on subchondral bone
- Increase joint congruence
What does the stiffness in compression of articular cartilage arise from?
- water association
2. inherent stiffness of proteoglycan
How does articular cartilage receive nutrients?
through synovial fluid
- movement and loading are critical for nutrients because there is no vascularization in articular cartilage
- -> water wash is essential=pushing water out of the proteoglycans when loading and movement occur
How is lubrication of a synovial joint achieved?
- lubrication=binding of cartilage proteoglycans + water
- passive shear forces on cartilage prompt the chondrocyte cells in it to produce proteoglycan 4, which is secreted into synovial fluid–> lubrication
What are the components of synovial fluid? Synovial membrane?
plasma filtrate (electrolytes + small molecules; fewer proteins)
synovial membrane:
- macrophage like cells that phagocytize debris
- cells secreting synovial proteins –> create viscosity (hyaluronic acid and lubricin)
How does articular cartilage initially behave under loading?
How does this change with increased duration of loading?
When would it be best to perform high impact activities?
initially stiff under loading.
With increased duration of loading, viscous flow increases deformation and relieves stress on the water–> decreased ability to absorb impact
high-impact activity is best performed in mornings
What are the 3 different types of lubrication?
- Boundary lubrication (non-moving joint): fluid clings by chemical attraction of lubricant to cartilage surface
- sliding hydrodynamic lubrication (moving): synovial fluid sucked into space (due to deformation and physical property of viscosity)
- squeeze film hydrodynamic lubrication (movement and impact loading): fluid forced out into joint space under load and sucked back in when unloaded
faster joint motion=lower viscosity
What types of things can result in cartilage destruction? (6)
- inhibition of nutrient flow (continuous compression, pannus adhesion in rheumatoid disease, synovial adhesion in prolonged immobilization)
- “Wear & tear” – repetitive microtrauma
- Repetitive intra-articular hydrocortozone injections
- Traumatic acute tears
- Crystal formation
- Septic destruction – pus is chondrolytic
What are 4 pathological reactions of cartilage?
- Increase/decrease in general/local growth [in juveniles]
- Destruction (crystals–> inflammation)
- Degeneration
- Peripheral proliferation – osteophytes at tiny marginal area of articular cartilage covered by perichondrium (osteophyses as a result of vascularization of subchondral marrow–> endochondral ossification)
How do intervertebral discs change from juvenile to adult?
- Juvenile vascularized from segmental arteries supplying adjacent bone
- Adult loss of vascularization & relative O2 concentration
- Nucleus pulposus of adult lumbar disc hypoxic
- Accounts for lack of success in injecting chondrocytes into nucleus pulposis
