Joint Physiology

Question 1

What is a fibrous joint?

Answer 1

Bones united by a fibrous tissue

Question 2

What is a cartilaginous joint?

Answer 2

bones united by cartilage

Question 3

What is the synovial membrane?

Answer 3

vascular connective tissue with capillary networks and lymphatics that lines the inner aspect of fibrous capsule
contains synovial cells (fibroblasts) which produces the synovial fluid

Question 4

What covers the articular surfaces of bones?

Answer 4

cartilage

Question 5

How do you differentiate between a simple and compound synovial joint?

Answer 5

simple - one pair of articular surfaces

Compound - more than one pair of articular surfaces

Question 6

What is the physiological functions of joints?

Answer 6

structural support

purposeful motion

Question 7

What are the 3 main roles of joints during purposeful motion?

Answer 7

• stress distribution
• confer stability
• joint lubrication

Question 8

What is joint lubrication provided by?

Answer 8

• cartilage interstitial fluid
• Synovium - derived hyaluronic acid (mucin) - a polymer of disaccharides
• Synovium-derived lubrcin - a glycoprotein

Question 9

What helps to confer stability?

Answer 9

shape of articular component
ligaments
synovial fluid

Question 10

What are the functions of synovial fluid?

Answer 10

• lubricates joints
• facilitates joint movements to reduce friction
• helps minimise wear and tear
• aids in nutrition of articular cartilage (avascular)
• supplies chondrocytes with O2 and nutrients and remove CO2 and waste products

Question 11

Give the general characteristics of synovial fluid?

Answer 11

• fills the joint cavity
• continuously replenished
• high viscosity (varies with joint movement)
• other constituents are derived from blood plasma
• contain few cells (mainly mononuclear leucocytes)

Question 12

How does the synovial fluid change during movement in terms of viscosity and elasticity?

Answer 12

Rapid movement is associated with decreased viscosity and increased elasticity

Question 13

What does normal synovial fluid look like?

Answer 13

clear and colourless

Question 14

What happens to the synovial fluid in pathology?

Answer 14

WBC count increased in inflam and sepsis

Turns red in traumatic synovial tap and in haemorrhage arthritis

Question 15

What are the main functions of articular cartilage and why?

Answer 15

low friction lubricated gliding surface to help prevent wear and tear
distributes contact pressure to subchondral bone

Question 16

Name the layers of articular cartilage from the articular surface down.

Answer 16

Superficial zone
Middle zone
Deep zone
Calcified zone

Question 17

In the different zone of articular cartilage, how do the collagen fibres differ?

Answer 17

organization of collagen fibres

relative content of cartilage component

Question 18

What is the articular cartilage made of? Describe it’s properties.

Answer 18

Hyaline cartilage

elastic and has sponge like properties

Question 19

What is the ECM of the articular cartilage made up of?

Answer 19

water 70% (most at top zone)
collagen type 2 20%
proteoglycans 10% (highest conc in middle and deep zone)

Question 20

What happens to the cartilage water, chondroitin and collagen content with age?

Answer 20

Decreases

Question 21

What is the purpose of water in the articular cartilage component, water?

Answer 21

Maintain the resiliency of the tissue and contribute to the nutrition and lubrication system

Question 22

What is the function of collagen in the articular cartilage?

Answer 22

Maintain cartilage architecture

Provides tensile stiffness and strength

Question 23

What is the proteoglycan component made up of?

Answer 23

mainly of glycosaminoglycan e.g. chondroitin sulphate

Question 24

Give the function of having proteoglycans in the cartilage.

Answer 24

Responsible for the compressive properties associated with load bearing

Question 25

What synthesises, organises, degrades and maintains the ECM of articular cartilage?

Answer 25

Chondrocytes

Question 26

The articular cartilage is avascular. How does it receive nutrients etc?

Answer 26

Chondrocytes receive nutrients and O2 via the synovial membrane

Question 27

The rate of degradation is/is not equal to the rate at which it is replaced?

Answer 27

Is - in normal jointa

Question 28

What could change the mechanical properties of cartilage?

Answer 28

changes in the relative amount of water, collagen and proteoglycans

Question 29

If the rate of ECM degradation exceeded the rate of it’s synthesis, what would happen?

Answer 29

joint disease

Question 30

What are the catabolic factors relating to cartilage matrix turnover?

Answer 30

Stimulate proteolytic enzymes and inhibit proteoglycan synthesis

Question 31

What are the anabolic factors relating to cartilage matrix turnover?

Answer 31

Stimulate proteoglycan synthesis and counteract effects of IL-1

Question 32

Name the markers of cartilage breakdown?

Answer 32

Increased levels of serum and synovial keratin sulphate

Increased levels of type 2 collagen in synovial fluid

Question 33

What may go wrong in a joint?

Answer 33

• cartilage and synovial composition and function deteriorate leading to wear and tear
• synovial cell proliferation and inflammation
• deposition of salt crystals
• injury and inflammation to periarticular structures

Question 34

What are the effects on the subchondral bone of cartilage deterioration?

Answer 34

• Cyst formation
• Sclerosis (increased density)
• Osetophyte formation (spiky bony formation into joint cavity)

Question 35

What shape are the crystals which cause gout and pseudogout?

Answer 35

Needle shaped uric acid crystals causes gouty arthritis

Rhomboid shaped calcium pyrophosphate crystals causes pseudo-gout