Joints, Synovial Fluid and Cartilage

Question 1

How can joints be classified?

Answer 1

• Fibrous
• Cartilaginous
• Synovial

Question 2

Give examples of fibrous joints.

Answer 2

• Periodontal ligament
• Cranial sutures
• Interosseous membranes

Question 3

What cartilage is present in primary cartilaginous (synchondrosis) joints?

Answer 3

Hyaline only

Question 4

What cartilage is present in secondary cartilaginous (symphysis) joints?

Answer 4

Hyaline and fibrocartilage

Question 5

Give an example of a primary cartilaginous joint.

Answer 5

Growth plates in long bones

Question 6

Give an example of a secondary cartilaginous joints.

Answer 6

Intervertebral disc

Question 7

What are the common features of synovial joints?

Answer 7

• Synovial cavity which is fluid filled
• Articular cartilage
• Fibrous capsule
• Synovial membrane

May also contain:

• Articular discs
• Ligaments
• Bursa

Question 8

What are the 6 types of synovial joint?

Answer 8

• Plane
• Hinge
• Pivot
• Condylar (ellipsoid)
• Saddle
• Ball and socket

Question 9

Give an example of a plane synovial joint.

Answer 9

Between tarsal bones

Question 10

Give an example of a synovial hinge joint.

Answer 10

Elbow

Question 11

Give an example of a synovial pivot joint.

Answer 11

Radius on ulna

Question 12

Give an example of a condylar synovial joint

Answer 12

Wrist

Question 13

Give an example of a saddle synovial joint.

Answer 13

Sternoclavicular joint

Question 14

Give an example of a ball and socket synovial joint.

Answer 14

Shoulder

Question 15

What contributes to joint stability?

Answer 15

• Shape of articulating surfaces
• Capsule and ligaments
• Muscles

Question 16

What is the main component of articular (hyaline) cartilage?

Answer 16

> 75% water (incompressible)

Question 17

Describe the layers of articular cartilage in synovial joints.

Answer 17

Superficial/tangential layer:
-flattened chondrocytes that produce collagen and glycoproteins (e.g. lubricin)

Transitional layer:
-Round chondrocytes that produce proteoglycans such as aggrecan

Change in collagen orientation from superficial to deep layers

Question 18

Glycoproteins

Answer 18

Proteins to which oligosaccharide chains are attached (more protein than carbohydrate)

Question 19

Give an example of a glycoprotein.

Answer 19

Lubricin

Question 20

Proteoglycans

Answer 20

Proteins that are heavily glycosylated (more carb than protein (a protein core to which one or more GAGs attach)

Question 21

Give an example of a proteoglycan

Answer 21

Aggrecan

Question 22

Glycosaminoglycans

Answer 22

Long unbranched polysaccharides which are highly polar and thus attract water

Question 23

Give an examples of a GAG

Answer 23

Hyaluronic acid

Question 24

What is the thickness of articular cartilages in the body?

Answer 24

• Average = 2mm
• Interphalangeal joints= 1mm
• Patella= 5-6mm

Question 25

What are the 3 As of cartilage?

Answer 25

- Avascular - Aneural - Alymphatic

Question 26

How are nutrients and waste transferred to and from cartilage?

Answer 26

Synovial fluid produced by the synovium (synovial membrane)

Question 27

What produced synovial fluid?

Answer 27

Synoviocytes in the synovium

Question 28

What are the features of the synovium?

Answer 28

- Contains synoviocytes - Rich capillary network - No epithelial lining Allows direct exchange of oxygen, carbon dioxide and metabolites between blood and synovial fluid

Question 29

What are the features of type A synoviocytes?

Answer 29

- Look like macrophages - Remove debris - Contribute to synovial fluid production

Question 30

What are the features of type B synoviocytes?

Answer 30

- Fibroblast like | - Main producer of synovial fluid

Question 31

What are the features of synovial fluid?

Answer 31

- Viscous fluid - Contains hyaluronic acid & lubricin - Fluid component (from blood plasma) - Small volumes (knee joint: ̴0.5 ml ) - Rapid turnover ( ̴2 hours)

Question 32

What are the functions of synovial fluid?

Answer 32

- Nutrition of cartilage - Removal of waste products - Lubrication leading to less friction and wear

Question 33

How does synovial fluid lubricate the joints?

Answer 33

Boundary -Glycoproteins such as lubricin bind to receptors on articular surfaces to form a thin film Hydrodynamic (like aquaplaning) - Surfaces kept apart by liquid pressure - Viscosity changes with load and velocity of movement Weeping -Fluid that is present in the cartilage is squeezed out into the synovial cavity to increase fluid volume

Question 34

What are bursa?

Answer 34

- Synovial membrane sacs which are fluid-filled - They reduce friction - Can become inflamed= bursitis

Question 35

How does ageing affect our joints?

Answer 35

Viscosity of synovial fluid increases - Slower joint movements - Reduced lubrication Water content of cartilage decreases -Reduced shock absorption Less protection of articular surfaces & increased risk of damage

Question 36

What pathological changes occur in osteoarthritis?

Answer 36

- Bone spur formation | - Narrowed discs