Joints, Synovial fluid and Cartilage

Question 1

What are the types of joints?

Answer 1

Fibrous - periodontal, cranial and interosseous membranes
Cartilaginous
Synovial

Question 2

What are the types of cartilaginous joints?

Answer 2

Primary - hyaline only (synchondrosis)
Secondary - hyaline and fibrocartilage (symphysis)

Question 3

What are common features of synovial joints?

Answer 3

Synovial cavity, articular cartilage, fibrous capsule, and synovial membrane (produces fluid)

Question 4

What contributes to joint stability?

Answer 4

Shape pf articulating surfaces
Fibrous capsule and ligaments
Muscles

Question 5

What are some important molecules for joints?

Answer 5

Glycosaminoglycans (GAGs) - highly polar, hyaluronic acid
Glycoproteins - proteins with carbs attached - lubricin
Proteoglycans - GAGs attached to protein - aggrecan

Question 6

What is articular cartilage made up of?

Answer 6

Hyaline cartilage
Articular cartilage is more than 75% water

Question 7

What are the layers of articular cartilage?

Answer 7

Superficial/ tangential layer - flattened chondrocytes produce collagen and glycoproteins
Transitional and deep layers - round chondrocytes produce proteoglycans

Question 8

What type of collagen type is in articular cartilage?

Answer 8

Type II
Change in collagen content and orientation from superficial to deep
Close to articular surface - parallel to surface
Middle - oblique fibres
Near bone - vertical fibres

Question 9

Describe the thickness of articular cartilage

Answer 9

Average is 2-3mm
Interphalangeal joint - 1mm
Patella is 5-6mm

Question 10

Describe the force on patella

Answer 10

Climbing stairs - 3 x body weight
Squatting - 7-8 x body weight
Jumping - up to 20 x body weight

Question 11

What are some features of cartilage?

Answer 11

Avascular
Aneural
Alymphatic

Question 12

What is important for delivering nutrients to cartilage?

Answer 12

Synovial fluid produced by synovial membrane

Question 13

Describe the synovium

Answer 13

Synoviocytes producing fluid
Rich capillary network
No epithelial lining
Which means there is direct exchange of O2, CO2, and metabolites

Question 14

Describe type A synoviocytes

Answer 14

Looks like macrophages, removes debris, and contribute to production of fluid (but not main type)

Question 15

Describe type B synoviocytes

Answer 15

Fibroblast like and main producer of synovial fluid

Question 16

Describe synovial fluid

Answer 16

Viscous fluid, hyaluronic acid and lubricin, and fluid component comes from blood plasma
Small volumes and rapid turnover

Question 17

What is the main function of synovial fluid?

Answer 17

Lubrication - less friction and wear

Question 18

What is the coefficient of friction?

Answer 18

Force to slide the surface/ load compressing the surface
In joints - 0.001-0.02

Question 19

What are the mechanisms of lubrication?

Answer 19

Fluid film
Weeping
Boundary

Question 20

Describe fluid film mechanism lubrication

Answer 20

Surfaces kept constantly apart by fluid
Much of load born by pressurised fluid

Question 21

Describe weeping mechanism of lubrication

Answer 21

Interstitial fluid is squeezed out of cartilage into synovial cavity to increase fluid volume

Question 22

Describe boundary mechanism of lubrication

Answer 22

Contact between surfaces, but coated in lipids, hyaluronic acid, and lubricin

Question 23

Describe bursae

Answer 23

Sacs of synovial membrane which are fluid filled and reduce friction
Can get bursitis

Question 24

What is the effect of ageing on joints?

Answer 24

Thinning of articular cartilage
Water content in cartilage decreased
Conc. of key molecules decrease
Increased collagen cross-linking due to formation of AGEs (advanced glycation end-products)
These all increase stiffness and brittleness, less able to absorb shock and increased risk of damage