Joints and Synovial Fluid and Cartilage

Question 1

what are the different types of joints?

Answer 1

• Fibrous - lots of collagen fibres, densely packed
• Cartilaginous - not that mobile but more mobile than fibrous
• Synovial - the most mobile ones – often these are the joints found in limbs

Question 2

what are examples of fibrous joints?

Answer 2

not much movement

Question 3

what are the 2 types of Cartilaginous joints and what makes them up?

Answer 3

• Primary c. joint: only hyaline cartilage
• Secondary c. joint: hyaline & fibrocartilage

Question 4

what is a Synchondrosis?

Answer 4

Primary cartilaginous joint

only hyaline cartilage

Question 5

what is a Symphysis?

Answer 5

Secondary cartilaginous joint

hyaline and fibrocartilage

Question 6

what are common features of a synovial joint?

Answer 6

Fibrous capsule around the synovial joint

Lined on inside with synovial membrane – in green

Articular cartilage on bone surface

In joint space you have synovial fluid

Question 7

what may some synovial joints contain?

Answer 7

Articular discs

Ligaments - can be in or out the joint capsule

Bursae - fluid filled pillows, variable around joints

Question 8

name this synovial joint

Answer 8

Plane

Question 9

name this synovial joint

Answer 9

Hinge

Question 10

name this synovial joint

Answer 10

Pivot

Question 11

name this synovial joint

Answer 11

Condylar (ellipsoid)

Question 12

name this synovial joint

Answer 12

Saddle

Question 13

name this synovial joint

Answer 13

Ball and socket

Question 14

what are factors that play a role in joint stability?

Answer 14

• Shape of articulating surfaces
• Capsule & ligaments
• Muscles

e.g. Shoulder is a shallow socket so very mobile but also unstable so can dislocate easily

Question 15

what cartilage is present in synovial joints?

Answer 15

Knee joint diagram, ooking from superior - lateral right and medial on left

Darker blue is articular cartilage – hyaline cartilage

Meniscus made of fibrocartilage

Wavy fibres in fibrocartilage is collagen, also get some collagen in the hyaline cartilage but cant see them in this photo

Fibrocartilage is stronger due to densely packed collagen

Question 16

what are the different layers of Articular cartilage (Hyaline cartilage)?

Answer 16

• Superficial/tangential layer: flattened chondrocytes that produce collagen and glycoproteins (e.g. lubricin)
• Transitional layer: round chondrocytes that produce proteoglycans such as aggrecan (really good at binding to water which is important to cartilage)
• Change in collagen orientation from superficial to deep layers
• >75% water (water = incompressible) - Water changes as you age. Water protects tissue from extreme compression and damage

Articular surface at top where the synovial fluid is

Chondrocytes round at bottom and flat at top – cartilage cells (they produce collage fibres, produce molecules that are important of healthy function of the cartilage called lubricin)

Thick black lines indicate the different collagen fibres

At top you find fibres parallel to the superficial surface, Oblique in the middle, Then vertical ones to the bone at the bottom. Makes sense to have the different fibre orientation. Collagen fibres good at resisting tensile strength

Question 17

‘Who is who’ of important molecules

When carbs (glycans) meet proteins …

what are Glycoproteins (e.g. lubricin)?

Answer 17

proteins to which oligosaccharide chains are attached, i.e. more a protein than a carbohydrate!

Question 18

‘Who is who’ of important molecules

When carbs (glycans) meet proteins …

what are Proteoglycans (e.g. aggrecan)?

Answer 18

proteins that are heavily glycosylated (= a protein core to which one or more GAGs attach), i.e. tend to be more carb than protein!

Question 19

‘Who is who’ of important molecules

When carbs (glycans) meet proteins …

what are Glycosaminoglycans or GAGs (e.g. hyaluronic acid)?

Answer 19

long unbranched polysaccharides, which are highly polar and thus attract water

Question 20

Articular cartilage - what is its thickness and forces?

Answer 20

average: 2-3 mm

interphalangeal joint: 1 mm (Small joints that are not load bearing are thinner than average)

patella: 5-6 mm (small bone but thick cartilage, forces acting on patella is high)

Question 21

whata re the 3 main features of Cartilage?

Answer 21

• Avascular
• Aneural
• Alymphatic

Question 22

Transport of nutrients to cartilage?

Removal of waste products?

how is it done?

Answer 22

Synovial fluid produced by synovial membrane (synovium)

tasks are done by the synovial fluid that surrounds the articular cartilage

Question 23

what is the Synovium?

Answer 23

The synovium, also called the synovial membrane, is the soft tissue. The synovium lines the entire inner surface of the joint, except where the joint is lined with cartilage

• Synoviocytes producing the fluid
• Rich capillary network
• No epithelial lining

→ Direct exchange of oxygen, carbon dioxide & metabolites between blood & synovial fluid

Question 24

what are the different types of Synoviocytes?

Answer 24

type A

type B

Question 25

what are the features of type A synoviocytes?

Answer 25

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

Question 26

what are the features of type B synoviocytes?

Answer 26

Fibroblast like Main producer of synovial fluid

Question 27

what are the features of Synovial fluid?

Answer 27

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

Question 28

what are the functions of synovial fluid?

Answer 28

* Nutrition of cartilage (articular c., menisci/discs) * Removal of waste products * Lubrication = less friction = less wear

Question 29

what are the different mechanisms of lubrication?

Answer 29

* 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 30

what is the coefficient of friction?

Answer 30

Result of these mechanisms working together Coefficient of friction – quantify the amount of friction between 2 surfaces Lower coefficient of friction is lower the friction

Question 31

what are Bursae?

Answer 31

* Synovial membrane * Fluid-filled * Reduce friction * Bursitis (inflammation, painful, not do their job properly)

Question 32

what happens to your joints as you age?

Answer 32

• 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 33

What happens in Osteoarthritis?

Answer 33

Common in elderly In effected joints – uncontrolled bone growth around the margins of the joint Bony spurs growing around the margin of the joint See the same in knee or hips joints affected by this It occurs when the protective cartilage that cushions the ends of your bones wears down over time