The Physiology of Cartilage Flashcards
What are the three types of cartilage
Hyaline (articular), fibrocartilage, elastic cartilage.
Where can hyaline cartilage be found
On the surfaces of moveable joints.
Which kind of forces can hyaline cartilage withstand
Compressive and tensile forces. It is load bearing.
What is the basketweave structure of collagen in hyaline cartilage
Hype two collagen linked by type nine collagen.
What is the appearance of chondrocytes in cartilage
They appear flat at the surface and rounded in the deep layers.
What is the role of chondrocytes
Chondrocytes are responsible for the synthesis and breakdown of ECM components in cartilage.
What is synthesised and secreted by chondrocytes into the ECM
Cartilage specific components such as type II collagen and aggrecan.
Are chondrocytes stable or unstable
Chondrocytes are unstable cells as they want to becomes fibroblasts - this would allow them to synthesise type I collagen and small PGs as opposed to type II collagen and aggrecan.
What type of enzymes are secreted by chondrocytes
Degradative enzymes such as collagenases, matrix metalloproteinases cathepsins.
Where can fibrocartilage be found
The meniscus and the intervertebral disc.
What are the roles of fibrocartilage
Support, prevention of bone to bone contact, spread of the load and limitation of movement.
What forces can fibrocartilage withstand
Tensile and compressive forces.
What is the orientation of collagen fibres in fibrocartilage
Collagen fibres are thick and have a clear parallel orientation and structure. Cells are often in rows.
Which types of cells - fibroblasts or chondrocytes - are present mostly in fibrocartilage
It is mainly fibroblasts however there are some chondrocytes.
Where can elastic cartilage be found
The auricle of the ear and the epiglottis
What is present in high contents in elastic cartilage
Elastin fibres
How does elastin in elastic cartilage show up in histology
Elastin shows up black in histology
What type of movement does elastic cartilage allow
Elastic cartilage is very good for flexible movement however is not good for load bearing.
Which types of cell synthesise elastin
Fibroblasts.
What are the roles of articular cartilage
To absorb and distribute load and protect the ends of bones. Along with synovial fluid it also creates a low friction surface for articulating joints.
What does synovial fluid contain
Hyaluronic acid.
Which cells produce synovial fluid
Synoviocytes of the synovial membrane.
What is the role of synovial fluid
Synovial fluid is the primary source of nutrition and removal of waste for cartilage cells.
What is the consistency of synovial fluid
When the joint is immobile, synovial fluid is viscous. When mobile, the viscosity is reduced to lubricate the joint.
What is the name of a condition in which the immune system attacks the synovium of joints
Rheumatoid arthritis.
What do connective tissues respond to
Their mechanical environment - they are not inert but living.
What makes cartilage thicker
Load bearing cartilage is ticker and stronger than non-load bearing cartilage.
What happens to cartilage in immobilised joints
Cartilage is lost because the cells are not receiving signals from the mechanical environment.
What is Wolff’s Law
“Form follows function” - if there is different load/mechanical stimulation on a joint this will affect its appearance.
How much movement is required per day to avoid disuse OP
Four cycles of strain per day - very little strain is needed to avoid disuse OP.
What is the function of a tendon
Connects muscle to bone
What is the function of a ligament
Connects bone to bone.
Where in a tendon may there be more proteoglycans
Where there is more compressive force applied, so when the tendon crosses a bone. If there is only tensile force there will be less PGs.
Which has a higher percentage of collagen, ligaments or tendons?
Tendons have a higher percentage of collagen compared to ligaments (more tensile forces)
Which has a higher percentage of proteoglycans, ligaments or tendons?
Ligaments have a higher percentage of proteoglycans compared to tendons (more compressive forces)
Which has more elastin, tendons or ligaments
Ligaments
What type of collagen has a higher percentage in both tendons and ligaments
Type I collagen.
What is cartilage thickness dependent on
Prevailing load
What is the result of excess or impact load
Matric damage and chondrocyte death.
What is the ratio of synthesis to break down in normal dynamic loading
Synthesis = breakdown normally
What is the relationship between synthesis and breakdown if there is greater loading
There is more synthesis than breakdown (synthesis > breakdown)
What is the relationship between synthesis and breakdown if there is less loading
There is more breakdown than synthesis (breakdown > synthesis)
Which cells control matrix synthesis and breakdown
Chondrocytes,
What are the two types of load on chondrocytes
Static and dynamic.
What is the relationship between static load and synthesis
Static load depresses synthesis.
What is the relationship between dynamic load and synthesis
Dynamic load stimulates synthesis.
What is mechanotransduction
The link between the mechanical environment of the cell and the cells response.
How is cartilage adapted to withstand load
It does not contain any vulnerable structures - it is avascular, aneural, alymphatic so blood vessels, nerves and lymphatic vessels cannot be damaged, and there is low cell density to cells do not become compressed.
What are the four principle components of articular cartilage
1) collagens
2) proteoglycans
3) interstitial fluid
4) chondrocytes.
What is the main type of collagen in hyaline cartilage
Type II
What is the main type of collagen in fibrocartilage
Type I
What type of collagen stabilises the basketweave structure of hyaline cartilage
Type 9
What is an example of a proteoglycan
Aggrecan
What is aggrecan composed of
Glucosaminoglycans (GAGs)
What is the charge of proteoglycans
Negatively charged
What does the negative charge of proteoglycans bring about
The negative charge attracts cations, particularly sodium ions, to the cartilage. This brings water with it and causes the proteoglycans to swell.
To what percentage of their total do proteoglycans swell when in the basketweave structure
20%
What is the result of papain treatment on cartilage
It causes chondrocytes to produce degragatory enzymes which damages proteoglycans.
What is the string and balloon model of articular cartilage
Type two collagen is stabilised by type nine collagen. The basketweave structure contains partially inflated PGs. There is lots of positive pressure.
What happens to the PGs if the collagen structure becomes damaged
The PGs inflate more.
What is the composition of the interstitial fluid dependent on
Proteoglycans as these are negatively charged so attract positive cations and repel negative anions.
What causes the composition of interstitial fluid to change
Different loads. It changes during static load as fluid is extruded.
What is the single resident cell type in hyaline cartilage
Chondrocytes.
When do chondrocytes proliferate
In the late stages of OA. In normal, healthy cartilage there is no chondrocyte division.
What is the rate of turnover of articular cartilage
Very slow.
Why would osteoarthritis be better termed osteoarthrosis
Because the condition is not initially inflammatory - it only becomes inflammatory in the late stages.
Is osteoarthritis considered a disease or a syndrome
A syndrome because it is a multifactorial condition - there are many factors which contribute.
What are the treatments for osteoarthritis
- Education
- “Prescription of exercise”
- Weight loss
What is the first macroscopic event in OA
Cartilage swelling - the cartilage becomes more hydrated.
How is OA cartilage different from aged cartilage
OA cartilage becomes more hydrated while age causes cartilage to become dehydrated.
Why does cartilage become more hydrated in OA
Because there is damage to the collagen basketweave structure which means more water is allowed to enter and the proteoglycans swell more. The cartilage becomes mechanically weakened.
