Joint physiology

Question 1

What are the three main types of joints?

Answer 1

Fibrous joint- syntharthrosis
Cartilaginous joint- amphiarthrosis
Synovial joint- diarthrosis

Question 2

Give an example of a fibrous joint.

Answer 2

The joints between the bones in the skull in an adult.

Question 3

Give 4 examples of cartilaginous joints.

Answer 3

Intervertebral discs
Pubic symphysis
Part of the sacroiliac joints
Costochondral joints

Question 4

What a) separates and b) unites a synovial joint?

Answer 4

a) A cavity

b) A fibrous capsule

Question 5

What lines the fibrous capsule in a synovial joint?

Answer 5

A synovial membrane

Question 6

Describe the synovial membrane

Answer 6

It is vascular connective tissue.
It has capillary networks and lymphatics
It has synovial cells (fibroblasts) which produce synovial fluid.

Question 7

What is a) a simple synovial joint and b) a compound synovial joint?

Answer 7

a) A synovial joint with one pair of articulating surfaces

b) A synovial joint with more than one pair of articulating surfaces

Question 8

What are the two main physiological functions of joints?

Answer 8

Structural support

Purposeful movement

Question 9

What are the roles of joints during purposeful movement?

Answer 9

Stress distribution
Confer stability
Lubricate the joint

Question 10

What takes up the greatest share of loading energy during purposeful movement?

Answer 10

The muscles and tendons spanning a joint

Question 11

Give three features of a joint which help it to confer stability

Answer 11

Shape of the articular component
Ligaments provide a secondary major stabilising influence
Synovial fluid acts as an adhesive seal that freely permits sliding movement between cartilaginous surfaces.

Question 12

What provides joint lubrication?

Answer 12

Cartilaginous interstitial fluid
Synovium-derived hyaluronic acid (mucin) which is a polymer of disaccharides
Synovium-derived lubricin- a glycoprotein

Question 13

What are the functions of synovial fluid?

Answer 13

Lubricates Joint
Facilitates joint movements - reduces friction
Helps minimise wear-and-tear of joints through efficient lubrication
Aids in the nutrition of articular cartilage
Supplies the chondrocytes (cartilage cells) with O2 and nutrients and remove CO2 and waste products

Question 14

Why does synovial fluid have a high viscosity?

Answer 14

Mainly because of the hyaluronic acid produced by synovial cells

Question 15

How does the viscosity and elasticity of synovial fluid vary with joint movement?

Answer 15

Rapid movement is associated with decreased viscosity and increased elasticity.

Question 16

What is the appearance of normal synovial fluid?

Answer 16

Clear and colourless

Question 17

What is the normal WBC count in synovial fluid?

Answer 17

It has <25/mm3

Question 18

What are the main functions of articular cartilage?

Answer 18

Provides a low friction lubricated gliding surface which helps to prevent wear and tear of joints.
Distributes contact pressure to subchondral bone.

Question 19

What is the special ECM of articular cartilage made of?

Answer 19

Predominantly of water (70%)
Collagen (20%)- mainly type II
Proteoglycans (10%)

Question 20

What is the function of the water in the articular cartilage?

Answer 20

It maintains the resiliency of the tissue and contributes to the nutrition and lubrication system.

Question 21

What is the function of the collagen in the articular cartilage?

Answer 21

Maintains cartilage architecture

Provides tensile stiffness and strength

Question 22

What is the function of the proteoglycan in articular cartilage?

Answer 22

It is responsible for the compressible properties associated with load bearing.

Question 23

What is responsible for synthesising, organising and degrading the cartilage ECM?

Answer 23

Chondrocytes.

Question 24

Where do the chondrocytes in the articular cartilage receive their oxygen and nutrients from?

Answer 24

Via the synovial fluid

Question 25

What breaks down the components of the ECM?

Answer 25

metalloproteinase proteolytic enzymes e.g. collagenase and stromelysin.

Question 26

What are the catabolic factors of cartilage matrix turnover and what do they do?

Answer 26

Tumour necrosis factor alpha
Interleukin 1
They stimulate proteolytic enzymes and inhibit proteoglycan synthesis.

Question 27

What are the anabolic factors of cartilage matrix turnover and what do they do?

Answer 27

Tumour growth factor-beta
Insulin-like growth factor 1
They stimulate proteoglycan synthesis and counteract the effects of IL-1

Question 28

Name two markers of cartilage degradation

Answer 28

Serum and synovial keratin sulphate

Type II collagen in synovial fluid