Physiology of Joints

Question 1

1111+What 2 main functions do joints provide for MSK system?

Answer 1

• Structural support
• Purposeful movement

Question 2

What 3 ways do joints help provide purposeful movement?

Answer 2

• Stress distribution
• Confer stability - shape of articular component, ligaments, synovial fluid (acts as an adhesive seal)
• Joint lubrication- cartilage interstitial fluid, synovium-derived hyaluronic acid (mucin - polymer of dissacharides), synovium-derived lubricin (glycoprotein)

Question 3

What type of bones have synovial joints?

Answer 3

Diarthrosis: articulation that permits free movement

Question 4

What type of bones have fibrous joints?

Answer 4

Synarthrosis: bones united by fibrous tissue, doesn’t usually allow any movement
- Examples are the bones of the skull in adults

Question 5

What types of bones have cartilaginous joints?

Answer 5

Amphiarthrosis: bones united by cartilage, allow limited movement
- Examples are the IV discs, pubic symphysis, part of the sacroiliac joints, costochondral joins

Question 6

What are bones separated and united by?

Answer 6

-Separated by a cavity (containing synovial fluid)
-United by a capsule (and other extra-articular structures e.g. ligaments, tendons and bursae)

Question 7

What is the synovial membrane?

Answer 7

A vascular connective tissue with capillary networks and lymphatics which lines the inner aspect of the fibrous capsule (about 60 µm thick in the human knee)

Question 8

What does the synovial membrane contain?

Answer 8

Synovial cells (fibroblasts) which produces the synovial fluid (about volume <3.5 m)

Question 9

What is the joint capsule and what does it contain?

Answer 9

-It isolates and covers the entire joint. -Contains an outer fibrous layer and an inner layer known as the synovial membrane.

Question 10

What are the articular surfaces of bones covered with?

Answer 10

Cartilage

Question 11

What is a simple synovial joint? Example

Answer 11

One pair of articular surfaces
-Metacarpophalangeal joint

Question 12

What is a compound synovial joint? Example

Answer 12

More than one pair of articular surfaces
-Elbow joint

Question 13

Describe characteristics synovial fluid in join cavity (3)

Answer 13

-Continuously replenished by the synovial membrane
-High viscosity - mainly due to the presence of hyaluronic acid (mucin) produced by the synovial cells
-The viscosity and elasticity of the synovial fluid varies with joint movement (Rapid movement is associated with decreased viscosity and increased elasticity)

Question 14

Is there uric acid present in synovial fluid?

Answer 14

Yes, derived by dialysis of blood plasma

Question 15

What is usual colour of synovial fluid and when does it turn red?

Answer 15

-Clear and colourless
-Turns red in traumatic synovial tap and in haemorrhagic arthritis

Question 16

Name 5 functions of synovial fluid

Answer 16

• Lubricates joint
• Facilitates joint movement - reduces friction
• Helps minimise wear-and-tear of joints through efficient lubrication
• Aids in the nutrition of articular chondrocytes
• Supplies the chondrocytes with O2 and nutrients and removes CO2 and waste products (articular cartilage is avascular)

Question 17

Name 3 functions of articular cartilage

Answer 17

• Provides a low friction lubricated gliding surface which helps prevent wear-and-tear of joints
• Distributes contact pressure to subchondral bone
• The fluid and solid phase of the cartilage plays a significant role in determining the mechanical properties of cartilage

Question 18

Describe structure of articular cartillage

Answer 18

• The articular cartilage is usually hyaline
• It is elastic and has sponge-like property
  -The zones differ in organisation of collagen fibres and relative content of cartilage components

Question 19

Describe the constituents of the ECM

Answer 19

-Water (70%) - maintains the resiliency of the tissue and contributes to the nutrition and lubrication system
-Collagen (20%) - mainly type II (elastic)
-Proteoglycans (10%) - responsible for the compressive properties associated with load bearing (act like ‘balloons’)

Question 20

What is the ECM synthesised by?

Answer 20

-Synthesized, organised and degraded by chondrocytes

Question 21

Is articular cartilage avascular?

Answer 21

True

Question 22

Where do chondrocytes receive their nutrients from?

Answer 22

Chondrocytes receive nutrients and O2 via the synovial fluid

Question 23

How can joint disease interrupt the normal cycle of joint reparation?

Answer 23

-In normal joints, the rate of ECM degradation doesn’t exceed the rate at which it is replaced
- Joint disease can occur if the rate of ECM degradation exceeds the rate of its synthesis

Question 24

Why does articular cartilage have poor healing/repair?

Answer 24

It is avascular

Question 25

What 4 things tend to go wrong in joint disease?

Answer 25

• Cartilage and synovial fluid decomposition and function deteriorate with age and repeated wear and tear → osteoarthritis
• Synovial fluid proliferation and inflammation → rheumatoid arthritis
• Deposition of salt crystals e.g. uric acid → gouty arthritis
• Injury and inflammation to periarticular structures can cause soft tissue rheumatism e.g. injury to the tendon causes tendonitis