The Physiology of Cartilage

Question 1

What are the three types of cartilage

Answer 1

Hyaline (articular), fibrocartilage, elastic cartilage.

Question 2

Where can hyaline cartilage be found

Answer 2

On the surfaces of moveable joints.

Question 3

Which kind of forces can hyaline cartilage withstand

Answer 3

Compressive and tensile forces. It is load bearing.

Question 4

What is the basketweave structure of collagen in hyaline cartilage

Answer 4

Hype two collagen linked by type nine collagen.

Question 5

What is the appearance of chondrocytes in cartilage

Answer 5

They appear flat at the surface and rounded in the deep layers.

Question 6

What is the role of chondrocytes

Answer 6

Chondrocytes are responsible for the synthesis and breakdown of ECM components in cartilage.

Question 7

What is synthesised and secreted by chondrocytes into the ECM

Answer 7

Cartilage specific components such as type II collagen and aggrecan.

Question 8

Are chondrocytes stable or unstable

Answer 8

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.

Question 9

What type of enzymes are secreted by chondrocytes

Answer 9

Degradative enzymes such as collagenases, matrix metalloproteinases cathepsins.

Question 10

Where can fibrocartilage be found

Answer 10

The meniscus and the intervertebral disc.

Question 11

What are the roles of fibrocartilage

Answer 11

Support, prevention of bone to bone contact, spread of the load and limitation of movement.

Question 12

What forces can fibrocartilage withstand

Answer 12

Tensile and compressive forces.

Question 13

What is the orientation of collagen fibres in fibrocartilage

Answer 13

Collagen fibres are thick and have a clear parallel orientation and structure. Cells are often in rows.

Question 14

Which types of cells - fibroblasts or chondrocytes - are present mostly in fibrocartilage

Answer 14

It is mainly fibroblasts however there are some chondrocytes.

Question 15

Where can elastic cartilage be found

Answer 15

The auricle of the ear and the epiglottis

Question 16

What is present in high contents in elastic cartilage

Answer 16

Elastin fibres

Question 17

How does elastin in elastic cartilage show up in histology

Answer 17

Elastin shows up black in histology

Question 18

What type of movement does elastic cartilage allow

Answer 18

Elastic cartilage is very good for flexible movement however is not good for load bearing.

Question 19

Which types of cell synthesise elastin

Answer 19

Fibroblasts.

Question 20

What are the roles of articular cartilage

Answer 20

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.

Question 21

What does synovial fluid contain

Answer 21

Hyaluronic acid.

Question 22

Which cells produce synovial fluid

Answer 22

Synoviocytes of the synovial membrane.

Question 23

What is the role of synovial fluid

Answer 23

Synovial fluid is the primary source of nutrition and removal of waste for cartilage cells.

Question 24

What is the consistency of synovial fluid

Answer 24

When the joint is immobile, synovial fluid is viscous. When mobile, the viscosity is reduced to lubricate the joint.

Question 25

What is the name of a condition in which the immune system attacks the synovium of joints

Answer 25

Rheumatoid arthritis.

Question 26

What do connective tissues respond to

Answer 26

Their mechanical environment - they are not inert but living.

Question 27

What makes cartilage thicker

Answer 27

Load bearing cartilage is ticker and stronger than non-load bearing cartilage.

Question 28

What happens to cartilage in immobilised joints

Answer 28

Cartilage is lost because the cells are not receiving signals from the mechanical environment.

Question 29

What is Wolff's Law

Answer 29

"Form follows function" - if there is different load/mechanical stimulation on a joint this will affect its appearance.

Question 30

How much movement is required per day to avoid disuse OP

Answer 30

Four cycles of strain per day - very little strain is needed to avoid disuse OP.

Question 31

What is the function of a tendon

Answer 31

Connects muscle to bone

Question 32

What is the function of a ligament

Answer 32

Connects bone to bone.

Question 33

Where in a tendon may there be more proteoglycans

Answer 33

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.

Question 34

Which has a higher percentage of collagen, ligaments or tendons?

Answer 34

Tendons have a higher percentage of collagen compared to ligaments (more tensile forces)

Question 35

Which has a higher percentage of proteoglycans, ligaments or tendons?

Answer 35

Ligaments have a higher percentage of proteoglycans compared to tendons (more compressive forces)

Question 36

Which has more elastin, tendons or ligaments

Answer 36

Ligaments

Question 37

What type of collagen has a higher percentage in both tendons and ligaments

Answer 37

Type I collagen.

Question 38

What is cartilage thickness dependent on

Answer 38

Prevailing load

Question 39

What is the result of excess or impact load

Answer 39

Matric damage and chondrocyte death.

Question 40

What is the ratio of synthesis to break down in normal dynamic loading

Answer 40

Synthesis = breakdown normally

Question 41

What is the relationship between synthesis and breakdown if there is greater loading

Answer 41

There is more synthesis than breakdown (synthesis > breakdown)

Question 42

What is the relationship between synthesis and breakdown if there is less loading

Answer 42

There is more breakdown than synthesis (breakdown > synthesis)

Question 43

Which cells control matrix synthesis and breakdown

Answer 43

Chondrocytes,

Question 44

What are the two types of load on chondrocytes

Answer 44

Static and dynamic.

Question 45

What is the relationship between static load and synthesis

Answer 45

Static load depresses synthesis.

Question 46

What is the relationship between dynamic load and synthesis

Answer 46

Dynamic load stimulates synthesis.

Question 47

What is mechanotransduction

Answer 47

The link between the mechanical environment of the cell and the cells response.

Question 48

How is cartilage adapted to withstand load

Answer 48

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.

Question 49

What are the four principle components of articular cartilage

Answer 49

1) collagens 2) proteoglycans 3) interstitial fluid 4) chondrocytes.

Question 50

What is the main type of collagen in hyaline cartilage

Answer 50

Type II

Question 51

What is the main type of collagen in fibrocartilage

Answer 51

Type I

Question 52

What type of collagen stabilises the basketweave structure of hyaline cartilage

Answer 52

Type 9

Question 53

What is an example of a proteoglycan

Answer 53

Aggrecan

Question 54

What is aggrecan composed of

Answer 54

Glucosaminoglycans (GAGs)

Question 55

What is the charge of proteoglycans

Answer 55

Negatively charged

Question 56

What does the negative charge of proteoglycans bring about

Answer 56

The negative charge attracts cations, particularly sodium ions, to the cartilage. This brings water with it and causes the proteoglycans to swell.

Question 57

To what percentage of their total do proteoglycans swell when in the basketweave structure

Answer 57

20%

Question 58

What is the result of papain treatment on cartilage

Answer 58

It causes chondrocytes to produce degragatory enzymes which damages proteoglycans.

Question 59

What is the string and balloon model of articular cartilage

Answer 59

Type two collagen is stabilised by type nine collagen. The basketweave structure contains partially inflated PGs. There is lots of positive pressure.

Question 60

What happens to the PGs if the collagen structure becomes damaged

Answer 60

The PGs inflate more.

Question 61

What is the composition of the interstitial fluid dependent on

Answer 61

Proteoglycans as these are negatively charged so attract positive cations and repel negative anions.

Question 62

What causes the composition of interstitial fluid to change

Answer 62

Different loads. It changes during static load as fluid is extruded.

Question 63

What is the single resident cell type in hyaline cartilage

Answer 63

Chondrocytes.

Question 64

When do chondrocytes proliferate

Answer 64

In the late stages of OA. In normal, healthy cartilage there is no chondrocyte division.

Question 65

What is the rate of turnover of articular cartilage

Answer 65

Very slow.

Question 66

Why would osteoarthritis be better termed osteoarthrosis

Answer 66

Because the condition is not initially inflammatory - it only becomes inflammatory in the late stages.

Question 67

Is osteoarthritis considered a disease or a syndrome

Answer 67

A syndrome because it is a multifactorial condition - there are many factors which contribute.

Question 68

What are the treatments for osteoarthritis

Answer 68

- Education - "Prescription of exercise" - Weight loss

Question 69

What is the first macroscopic event in OA

Answer 69

Cartilage swelling - the cartilage becomes more hydrated.

Question 70

How is OA cartilage different from aged cartilage

Answer 70

OA cartilage becomes more hydrated while age causes cartilage to become dehydrated.

Question 71

Why does cartilage become more hydrated in OA

Answer 71

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.