Joints, synovial fluid and cartilage

Question 1

What are examples of fibrous joints?

Answer 1

• Periodontal ligament
• Cranial sutures
• Interosseous membranes

Question 2

What is an example of a primary cartilaginous joint?

Answer 2

Within a bone at the epiphysis (remember: this joint only has hyaline cartilage present in the joint)

Question 3

What is an example of a secondary cartilaginous joint?

Answer 3

Between vertebral bodies (remember this joint has hyaline and fibrocartilage present at the joint)

Question 4

What are common features of a synovial joint?

Answer 4

• Articular discs
• Ligaments
• Bursae
• Synovial cavity/membrane

Question 5

Types of synovial joints?

Answer 5

• Plane
• Condylar
• Hinge
• Saddle
• Pivot
• Ball and socket

Question 6

What layers exist in articular (hyaline) cartilage of synovial joints and what are there features?

Answer 6

• Superficial layer: Flattened chondrocytes, produce collagen and glycoproteins (eg lubricin)
• Transitional layer: round chondrocytes, produce proteoglycans (eg aggrecan)
• > 75% water (so incompressible)

Question 7

Is collagen thickness the same at all articular cartilage sites?

Answer 7

No, varies.

Question 8

How does synovial joint remove waste and transport nutrients if its avascular/aneural/alymphatic?

Answer 8

Synovial fluid produced by synovium

Question 9

There are two types of synoviocytes in the synovium - A and B. What are their roles?

Answer 9

Type A: Remove debris, help produce synovial fluid

type B: Main synovial fluid producer

Question 10

What are the functions of synovial fluid?

Answer 10

• Nutrition of cartilage
• Remove waste products
• Lubrication (less friction = less wear)

Question 11

How does the lubrication work? (think about Boundary, hydrodynamics, weeping)

Answer 11

Boundary: glycoproteins such as lubricin bind to receptors on articular surfaces forming thin film

Hydrodynamic (like aquaplaning): surfaces separated by liquid pressure. Viscosity changes with load and viscosity of movement

Weeping: fluid present in cartolage squeezed into synovial cavity to inc fluid volume

Question 12

What happens upon ageing to synovial joints?

Answer 12

Viscosity of synovial fluid increases (slower movements, less lubrication)

Water content of cartilage dec. (less shock absorption)

Less protection of articular surfaces and inc risk of damage