Joints, Synovial Fluid and Cartilage

Question 1

What are the different types of joint?

Answer 1

Fibrous - bone to bone with fibrous connective tissue and collagen fibres between

Cartilaginous - bone to bone with cartilage between

Synovial

Question 2

Give an example of a fibrous joint

Answer 2

Periodontal ligament
Cranial sutures
Interosseous membrane

Question 3

Give an example of a cartilaginous joint

Answer 3

Primary cartilage - synchondrosis

Secondary cartilaginous - symphysis

Question 4

What is the difference between primary and secondary cartilaginous joints?

Answer 4

Primary cartilaginous contain only hyaline cartilage, secondary cartilaginous contain hyaline and fibrocartilage

Question 5

What are the common features of synovial joints?

Answer 5

Synovial cavity, fluid filled
Articular cartilage
Fibrous capsule
Synovial membrane

May also contain articular discs, ligaments and bursae

Question 6

What is joint stability dependent on?

Answer 6

Shape of articulating surfaces
Capsule and ligaments
Muscles

Question 7

What are the types of synovial joints?

Answer 7

Plane
Hinge
Pivot
Condylar
Saddle
Ball and socket

Question 8

What is the structure of articular cartilage?

Answer 8

Superficial/tangential layer - flattened chondrocytes that produce collagen and glycoproteins
Transitional layer - round chondrocytes that produce proteoglycans
Change in collagen orientation from superficial to deep layers

Question 9

What percentage of articular cartilage is made up of water?

Answer 9

> 75%

Question 10

What are glycoproteins?

Answer 10

Proteins to which oligosaccharide chains are attached, more protein than carbohydrate e.g. lubricin

Question 11

What are proteoglycans?

Answer 11

Proteins that are heavily glycosylated i.e. a protein core to which one or more GAGs attach, tend to be more carbohydrate than protein e.g. aggrecan

Question 12

What are glycosaminoglycans?

Answer 12

Long unbranched polysaccharides which are highly polar and attract water e.g. hyaluronic acid

Question 13

How are nutrients transported to cartilage and waste products removed?

Answer 13

Via synovial fluid produced by the synovial membrane, as cartilage is avascular, aneural and alymphatic

Question 14

What are the features of synovium?

Answer 14

Synoviocytes produce the fluid
Rich capillary network
No epithelial lining
Direct exchange of oxygen, carbon dioxide and metabolites between blood and synovial fluid

Question 15

What are the functions of type a synoviocytes?

Answer 15

Look like macrophages
Remove debris
Contribute to synovial fluid production

Question 16

What are the functions of type b synoviocytes?

Answer 16

Fibroblast like

Main producer of synovial fluid

Question 17

What are the features of synovial fluid?

Answer 17

Viscous fluid
Contains hyaluronic acid and lubricin
Fluid component from blood plasma
Present in small volumes e.g. 0.5ml in knee joint 
Rapid turnover - around 2 hours

Question 18

What are the functions of synovial fluid?

Answer 18

Nutrition of cartilage and menisci/discs
Removal of waste products
Lubrication (results in less friction and less water)

Question 19

What is boundary lubrication?

Answer 19

Glycoproteins such as lubricin bind to receptors on the articular surfaces to form a thin film

Question 20

What is hydrodynamic lubrication?

Answer 20

Like aquaplaning - surfaces are kept apart by liquid pressure, viscosity changes with load and velocity of movement

Question 21

What is weeping lubrication?

Answer 21

Where fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume

Question 22

What are the features and functions of the bursae?

Answer 22

Fluid filled
Synovial membrane
Reduce friction
Cause bursitis when inflammation/irritation occurs

Question 23

What is the effect of ageing on the viscosity of synovial fluid?

Answer 23

Viscosity of synovial fluid increases with age, resulting in slower joint movements and reduced lubrication

Question 24

What is the effect of ageing on the water content of cartilage?

Answer 24

Water content of cartilage decreases with ageing, resulting in reduced shock absorption

Question 25

What do the effects of ageing on the viscosity of synovial fluid and water content of cartilage result in?

Answer 25

Less protection of articular surfaces and increased risk of damage