Biomechanics unit 2 - biomech of skeletal muscle tissue deck 4 Flashcards
What is the most common protein in the human body?
Collagen
What is articular cartilage made up of?
An organic matrix of non-cellular material, interspersed with cells and fluid.
What is the organic matrix of non-cellular material in articular cartilage primarily made up of?
Collagen
In articular cartilage describe the structure of collagen
It is structured into strong, fine collagen fibrils
What % of the dry and wet weight of articular cartilage is collagen?
- 50-80% of the dry weight
- 10-20% of the wet weight
What are the collagen fibrils enmeshed (entangled) in, in articular cartilage ?
A concentrated solution of proteoglycans
What part of articular cartilage has the highest concentration of proteoglycans and what has the lowest concentration ?
- Highest concentration - The middle zone
- Lowest concentration - the deep layers adjacent to the bone
What % of the wet weight of articular cartilage is made up of proteoglycans ?
3-10%
What are the sparsely distributed cells in articular cartilage called?
Chondrocytes
What % of the articular cartilages tissue volume does chondrocytes account for ?
<10%
What part of the articular cartilage is the highest concentration of chondrocytes found ?
The deeper layers adjacent to the bone
What is the function of chondrocytes ?
They manufacture, secrete and maintain the organic matrix of articular cartilage
What is the interstitial fluid found in articular cartilage ?
It is the fluid that occupies the spaces in the matrix, it is mainly made up of water. (the white spaces)
What % of the wet and dry weight of articular cartilage does the interstitial fluid make up?
- 68-85% of wet weight
- 0% of dry weight
What 3 zones can the articular cartilage be split up into?
- Superficial tangential zone
- Middle zone
- Deep zone
Structurally, articular cartilage can be divided into three zones according to what?
The orientation and density of chondrocytes and the orientation of the collagen fibres.
Describe the orientation and appearance of chrondrocytes and collagen fibrils in the superficial tangential zone of articular cartilage
- The collagen fibrils are tightly woven into sheets arranged parallel to the articular surface
- The chondrocytes are oblong with their longitudinal axes aligned parallel to the articular surface.
Describe the orientation and appearance of chrondrocytes and collagen fibrils in the middle zone of articular cartilage
- The collagen fibrils are arranged more randomly but still broadly parallel to the articular surface. They are less densely packed to accommodate the high concentration of proteoglycans
- The chondrocytes are circular and randomly distributed.
Describe the orientation and appearance of chrondrocytes and collagen fibrils in the deep zone of articular cartilage
- The collagen fibrils are arranged in larger fibre bundles that are anchored in the underlying bone tissue (fibre bundles perpendiculat to articular surface), thereby attaching the articular cartilage to the bone.
- The chondrocytes are arranged in loose columns aligned perpendicular to the line dividing the articular cartilage and the underlying bone.
What is below the deep zone of articular cartilage ?
A thin layer of calcified cartilage which gradually merges into the underlying subchondral bone.
What is the name given to the interface between the articular cartilage and calcified cartilage beneath it?
The tidemark
Describe creep behaviour of a viscoelastic material
When the load is first applied the material will deform quite rapidly. Followed by a slowly (creeping) increasing deformation.
(pic shows articular cartilage under a constant compressive load over a period of time)
Explain why creep behaviour occurs in articular cartilage ( / viscoelastic material)
Consider its composition and structure (i.e. high composition of intersistial fluid)
During the initial rapid deformation (between point A and B), fluid is rapidly forced out of the articular cartilage. As the amount of fluid remaining in the articular cartilage diminishes, so the rate of expellation decreases until at equilibrium (point C) fluid flow ceases completely and the applied load is borne entirely by the solid matrix.
When does stress relaxation occur in a viscoelastic material, such as articular cartilage?
When the material is kept at a constant deformation.
Describe what stress relaxation is
- This is where the stress is reduced over time as the material is maintained at a constant strain (deformation).
- In other words if a material is deformed to a certain degree the load required to maintain that deformation decreases with time.
Pic shows the stress in articular cartilage as it is maintained at a constant deformation over a period of time.
Explain why stress relaxation occurs in articular cartilage ( / viscoelastic material)
Consider its composition and structure.
During the initial deformation (between points A and B) interstitial fluid is forced out as the surface layers are compacted. Because of the large frictional drag associated with the flow of fluid through the solid matrix, large loads are needed to compress the tissue.
During the stress relaxation phase (from point B onwards) the stress required to maintain the deformation is reduced as fluid is no longer being forced out and the fluid within the tissue is redistributed from the least compacted deeper layers to the most compacted surface layers within the articular cartilage.
