Articular Cartilage Flashcards
What are the 3 types of cartilage?
hyaline
elastic
fibrocartilage
What does hyaline cartilage do?
covers tha articular surface of bones in synovial joints
What does elastic cartilage do?
forms structures like the outer ear, epiglottis
What structures are made from fibrocartilage?
symphysis pubis, intervertebral discs
What is articular cartilage?
a form of hyaline cartilage found on the articulating ends of bones in synovial joints
What are the two main roles of articular cartilage?
shock absorption
reducing joint friction
What is the gross composition of articular cartilage?
organic matrix of non-cellular material interspersed with cells and fluid
What is the organic matrix of non-cellular material in cartilage made from?
Collagen organised into fine collagen fibrils
What fluid is present around the collagen fibrils?
concentrated proteoglycans
Which layer of cartilage are proteoglycans most abundant?
middle layer
less concentrated towards bone
What is the name for the sparsely distributed cells of articular cartilage?
chondrocytes
What happens to the abundance of chondrocytes as you move towards the bone?
increases
What is made by chondrocytes?
collagen (the organic matrix)
What is the interstitial fluid in the matrix made from?
water
What are the 3 zones of cartilage called?
superficial tangential
middle
deep
What is the structure of the superficial tangential zone?
tightly woven collagen fibrils in sheets parallel to the articular surface
chondrocytes are oblong with parallel axes to the surface
What is the structure of the middle zone?
more randomly arranged collagen but broadly arranged parallel to the articular surface
less densely packed to accommodate proteoglycans high concentration
chondrocytes are circular and randomly distributed
What is the structure of the deep zone?
collagen fibrils in large fibre bundles that are anchored in the underlying bone tissue - attaching cartilage to bone.
chondrocytes are aligned perpendicular to the articular surface
What is the tidemark?
the interface between a thin layer of calcified cartilage below the deep zone which gradually merges into the subchondral bone.
What does viscoelastic behaviour mean?
It means that the response of the material varies according to the length of time it is loaded and the rate at which it is loaded.
What happens when a load is removed from a viscoelastic material?
it will return to its original shape - but not immediately
What is creep?
Creep occurs when a viscoelastic material is subject to a constant load - initially rapid deformation occurs, followed by slowly increasing deformation .
Why does creep occur?
During initial deformation, fluid is rapidly pushed out of the cartilage. As the fluid is pushed out the rate of expulsion decreases, as does the fluid remaining until equilibrium is reached
What is stress relaxation?
Stress relaxation occurs when a viscoelastic material is kept at a constant deformation - if a material is deformed to a certain degree the load required to maintain that deformation decreases with time
Why does stress relaxation occur?
Stress relaxation occurs as during initial deformation fluid is forced out of the joint - due to friction of forcing out fluid a large load is needed.
during stress relaxation the fluid is no longer being forced out so the stress required to maintain a deformation decreases
What are the 3 types of lubrication?
elastohydrodynamic
boosted
boundary
What is elastohydrodynamic lubrication?
This happens when two surfaces are lubricated by a film of fluid as they move relative to one another
What is squeeze film lubrication?
elastohydrodynamic lubrication when surfaces are compressed together
What is hydrodynamic lubrication?
lubrication when two surfaces slide over each other forming a wedge of fluid which generates a lifting pressure
What is boosted lubrication?
when two surfaces are forced together over a period of time, eventually the lubricant will be completely depleted
the articular cartilage surface is selectively permeable - so small molecules are forced through, leaving only large solute molecules behind
this leaves a thick, enhanced lubricant capable of supporting large loads
What is boundary lubrication?
Boundary lubrication is when loads are large enough and sustained for long enough, the fluid will will become completely depleted.
lubricant molecules attach themselves to the articular surfaces and create a BOUNDARY LAYER like a non-stick frying pan.
What protein is involved in boundary lubrication?
lubricin
