Joints, synovial fluid and cartilage

Question 1

What are the 3 structural types of joints?

Answer 1

Fibrous

Cartilaginous

Synovial

Question 2

Describe what fibrous joints are

Answer 2

Union of two bones where they are connected by dense fibrous connective tissue - essentially just collagen

This makes them very strong, and not very movey

Question 3

Where are fibrous joints found?

Answer 3

Cranial sutures

Periodontal ligament

Interosseus membranes

Question 4

What are cartilaginous joints?

Answer 4

Joints in which the bones are linked by cartilage

2 types:

Synchondrosis / primary cartilaginous

Symphysis / secondary cartilaginous

Question 5

What is the difference between synchondrosis and symphysis?

Answer 5

Synchondrosis (primary):

• only hyaline cartilage

Symphysis (secondary):

• hyaline cartilage & fibrocartilage

Question 6

Give an example of where a synchondrosis joint is found

Answer 6

Synchondrosis (primary)

Growth plate of growing long bones

Question 7

Give an example of where you would find a symphysis joint

Answer 7

symphysis (secondary cartilaginous)

Intervertebral discs

Question 8

Identify the main features of a synovial joint

Answer 8

Question 9

Aside from the common features in the diagram before - what else may synovial joints contain?

Answer 9

Articular discs - eg meniscus of knee

Ligaments - can be within or outside capsule

Bursae

Question 10

What are bursae?

Answer 10

Little fluid filled pillow things that are found round joints

Act as cushion things

Question 11

What are the types of synovial joint?

Answer 11

Plane

Hinge

Pivot

Condylar (ellipsoid)

Saddle

Ball & socket

Question 12

identify the types of joint shown in each example

Answer 12

Question 13

What determines the stability of joints?

Answer 13

1) The shape of articulating surfaces
* Shallow means more mobile joint but less stable
2) Ligaments and capsules surrounding the joint
3) Muscles surrounding the joint

Question 14

What type of cartilage is ‘articular cartilage’?

Answer 14

Hyaline cartilage

Question 15

If viewed histologically - what layers are present in articular cartilage?

Answer 15

Superficial / tangential layer

Transitional layer

Question 16

What are the main features of the superficial (tangential) layer of articular cartilage?

Answer 16

Layer closest to the articular surface

Identifiable by the presence of Lots of flat chondrocytes

These chondrocytes produce collagen and glycoproteins (eg lubricin)

Question 17

What are the main features of the transitional layer of articular cartilage?

Answer 17

Fewer and more rounded looking chondrocytes

These produce proteoglycans such as aggrecan

Question 18

How does the orientation of chondrocytes change as you move from superficial to deep?

Answer 18

Question 19

What is hyaline cartilage predominantly made up of?

Why is this suited for its structure?

Answer 19

>75% water

Water is incompressible

Question 20

Whats the difference between proteoglycans, glycoproteins and Glycosaminoglycans (GAGs)?

Answer 20

Glycoproteins - proteins to which oligosaccharide chains are attached

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

Glycosaminoglycans or GAGs (e.g. hyaluronic acid): long unbranched polysaccharides, which are highly polar and thus attract water

Question 21

How thick is articular cartilage

Answer 21

average: 2-3 mm

(interphalangeal joint: 1 mm)

(patella: 5-6 mm)

Question 22

Cartilage has 3 overall distinct features which separate it from other types of tissue

What are these?

Answer 22

Cartilage is:

• avascular
• aneural
• alymphatic

In reality - at the peripheries of cartilage - you find things like blood vessels etc but in general this is true so shut up

Question 23

If cartilage is avascular and alymphatic - then how does it transport nutrients and waste to/from its cells?

Answer 23

Through synovial fluid

Question 24

What produces synovial fluid?

Answer 24

Synoviocytes in the synovium (synovial membrane)

Question 25

Describe the main features of the synovium?

Answer 25

Synovium = synovial membrane Contains synoviocytes Has a rich capillary network Has **no** epithelial lining

Question 26

How is the transport of nutrients between blood and the synovium done?

Answer 26

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

Question 27

What are the different types of synoviocytes?

Answer 27

Type A & B Type A - Remove debris and contribute to SF production Type B - Main producer of SF

Question 28

What is synovial fluid? What is it made of?

Answer 28

Viscous fluid Made up of Hyaluronic acid & lubricin Also has fluid component from plasma Rapid turnover (around 2 hours)

Question 29

What type of cells do type A & B synoviocytes resemble?

Answer 29

Type A synoviocytes - resemble Macrophages Type B synoviocytes - resemble fibroblasts

Question 30

What are the functions of synovial fluid?

Answer 30

Nutrition of cartilage Removal of waste products Lubing everything up xx

Question 31

What are the 3 types of lubrication?

Answer 31

Boundary lubrication Hydrodynamic lubrication Weeping lubrication

Question 32

What is boundary lubrication?

Answer 32

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

Question 33

What is hydrodynamic lubrication?

Answer 33

Think of aquaplaning Surfaces kept apart by liquid pressure Viscosity changes with load and velocity of movement

Question 34

What is weeping lubrication?

Answer 34

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

Question 35

What is the inflammation of bursae called?

Answer 35

Bursitis funnily enough

Question 36

How does ageing affect joints?

Answer 36

2 main things that change... 1) **Increased viscosity** of synovial fluid * Slower movements, less lubrication 2) **Decreased water content** of articular cartilage * Reduced shock absorption Both these changes mean there is less protection to older joints