Joints, Synovial Fluid and Cartilage

Question 1

Functions of skeletal system

Answer 1

• Supports the body
• Facilitates movement
• Protects internal organs

Question 2

Structural classifications of joints

Answer 2

• Fibrous
• Cartilagenous
• Synovial

Question 3

Fibrous joint

Answer 3

• Fibrous CT with dense collagen fibres between bones
• Fairly immobile

E.g.

• Periodotal ligament
• Cranial sutures
• Interosseus membranes

Question 4

Cartilagenous joint

Answer 4

• Cartilage between bones (collagen fibres not dense)
• Immobile (> fibrous)

Primary/Synchondrosis

• Hyaline cartilage only
• Growth plate (ossify)
• Immovable

Secondary/Symphysis

• Hyaline and fibrocartilage
• Usually permanent
• Present in midline of body
• Allow little movement

Question 5

Synovial joint

Answer 5

• Fibrous capsule lined with synovial membrane
• Articular cartilage (not lined)
• Fluid-filled synovial cavity

May contain:

• Articular (fibrocartilage) discs
• Ligaments
• Bursae

Question 6

Types of synovial joint

Answer 6

Plane: carpals of hand
Hinge: knee
Pivot: elbow
Condylar (ellipsoid): radio-carpal
Saddle: thumb
Ball and socket: shoulder

Question 7

Joint stability

Answer 7

• Shape of articulating surfaces
• Capsule and ligaments
• Muscles

Question 8

Articular (hyaline) cartilage: Thickness and water content

Answer 8

Av. thickness: 2-3 mm

• Interphalangeal: 1mm
• Patella: 5-6mm

> 75% water (incompressible)

Question 9

Articular (hyaline) cartilage: Histological layers

Answer 9

Superficial/tangential layer

Transitional layer

Question 10

Superficial/tangential layer

Answer 10

• Flattened chondrocytes

- Produce collagen and glycoproteins (lubrican)

Question 11

Transitional layer

Answer 11

• Round chondrocytes

- Produce proteoglycans (aggrecan)

Question 12

Articular (hyaline) cartilage: collagen orientation

Answer 12

Superficial: parallel to articular surface
Transitional: oblique
Deep: perpendicular to articular surface

Question 13

Articular (hyaline) cartilage: function

Answer 13

Provide a smooth, lubricated surface

• Low friction articulation
• Transmission of loads to underlying subchondral bone

Question 14

Glycoproteins

Answer 14

E.g. lubrican

• Proteins with oligosaccharide chains
• Protein > carb

Question 15

Proteoglycans

Answer 15

E.g. aggrecan

• Highly glycosylated protein
• Carb > protein

Question 16

Glycosaminoglycans (GAGs)

Answer 16

E.g. hyaluronic acid

• Long unbranched polysaccharides
• Highly polar (attract water)

Question 17

Cartilage nutrition

Answer 17

• Avascular (except at periphery)
• Aneural
• Alymphatic

Question 18

Synovium

Answer 18

Synovial membrane

• Synoviocytes (Type A and B) produce synovial fluid
• Rich capillary network
• No epithelial lining
• Direct exchange of O2, CO2 and metabolites between blood and synovial fluid

Question 19

Type A synoviocytes

Answer 19

• Remove debris

- Contribute to synovial fluid production

Question 20

Type B synoviocytes

Answer 20

• Main producer of synovial fluid

Question 21

Constituents of synovial fluid

Answer 21

Viscous fluid

• Hyaluronic acid
• Lubricin
• Fluid component from blood plasma (small volumes, rapid turnover)

Question 22

Function of synovial fluid

Answer 22

• Nutrition of cartilage
• Removal of waste products
• Lubrication: less friction

Question 23

Types of lubrication

Answer 23

• Boundary: glycoproteins (lubrican) bind to articular surface receptors (thin film)
• Hydrodynamic: fluid pressure separates surfaces
• Weeping: increased load squeezes fluid out of cartilage

Question 24

Viscosity of synovial fluid increases

Answer 24

Increased load

Decreased speed

Question 25

Bursae

Answer 25

Fluid-filled synovial membraned (pillows) - Reduce friction in areas with a high risk of friction - Bursitis

Question 26

Ageing changes

Answer 26

- Increased viscosity of synovial fluid | - Water content decreases (reduced shock absorption)