Joints, synovial fluid and cartilage

Question 1

Where do you find fibrous joints?

Answer 1

• Sutures in the skull
• Peridontal ligament - anchors each tooth to the jaw
• Interosseous membranes - found between bones

Question 2

Name the 2 different types of cartilaginous joints

Answer 2

• Primary cartilaginous joint or Synchondrosis
• Secondary cartilaginous joint or Symphysis

Question 3

Synchondrosis/primary c. joint

Answer 3

• Contains 1 type of cartilage = hyaline
• Found in growing long bones

Question 4

Symphysis / secondary c. joint

Answer 4

• Contains 2 types of cartilage = hyaline and fibrocartilage
• Found between vertebrae

Question 5

What is the most mobile type of joint?

Answer 5

Synovial

Question 6

Describe a synovial joint

Answer 6

Fibrous capsule surrounding the synovial joint that is lined on the inside with a synovial membrane

Articular cartilage covers the bone surfaces and in between in the joint space there is synovial fluid for lubrication

Question 7

What types of things stabilise a joint? (3)

Answer 7

The shape of the articulating surfaces

Capsules and ligaments surrounding the joint - want these to be strong

Muscles

Question 8

Mechanically which is stronger, hyaline cartilage or fibrocartilage?

Answer 8

Fibrocartilage

Question 9

What are the 2 different layers in articular cartilage called?

Answer 9

• Superficial layer
• Transitional layer

Question 10

Describe the Superficial/tangential layer

Answer 10

Has flattened chondrocytes that produce collagen fibres and glycoproteins (e.g lubricin - for lubrication)

• A glycoprotein is a compound containing carbohydrate covalently linked to protein

Question 11

Describe the Transitional layer

Answer 11

Round chondrocytes that produce proteoglycans such as aggrecan (good at binding to water)

Question 12

What is a proteoglycan?

Answer 12

• It is a subtype of glycoprotein
• The difference is that the carbohydrate units are polysaccharides that contain amino sugars. These polysaccharides are also known as glycosaminoglycans i.e. they tend to be more carb than protein!

Question 13

What is a Glycoprotein?

Answer 13

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

Question 14

What is a Glycosaminoglycans or GAGs?

Answer 14

Long unbranched polysaccharides, which are highly polar and thus attract water e.g. hyaluronic acid

These are found in proteoglycans such as the ones in the transitional layer of articular cartilage

Question 15

Average cartilage thickness around the body

Answer 15

• 2-3 mm
• In weight bearing joints it will be thicker i.e. the knee = 5-6 mm because the force on this joint is very high in certain movements

Question 16

What produces synovial fluid?

Answer 16

Synovial membrane (synovium)

• Synoviocytes within the synovium produce the fluid

Question 17

3 A’s of cartilage

Answer 17

• Avascular
• Aneural
• Alymphatic

Question 18

What type of tissue makes up synovial fluid?

Answer 18

Synovium

Question 19

Type A synoviocyte

Answer 19

• Remove debris/waste
• Look like macrophages
• Contribute to synovial fluid production but not main producers

Question 20

Type B synoviocyte

Answer 20

Main producer of synovial fluid

• Fibroblast-like cells

Question 21

Functions of synovial fluid

Answer 21

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

Question 22

What is the simplest way of lubricating the articular surface?

Answer 22

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

Question 23

3 mechanisms of lubrication of joints

Answer 23

• Boundary
• Hydrodynamic
• Weeping

These work together in a healthy joint to lubricate it nicely

Question 24

Hydrodynamic (Like aquaplaning)

Answer 24

Aquaplaning - in a car when you lose the contact between the wheels and the road. In bones, this is good as it protects the cartilage. Surfaces are kept apart by liquid pressure. Viscosity changes with load and velocity of movement

Question 25

Weeping lubrications

Answer 25

Synovial fluid squeezed out of cartilage into the joint space - increasing the volume of the synovial fluid here - this happens when you have high pressure on the joint

Question 26

What are Bursae?

Answer 26

• They surround synovial joints
• Fluid-filled sac made up of synovial membrane with fluid inside (like a pillow).
• They tend to sit in areas where you have a high risk of friction i.e. between tendon and bone
• Bursitis = inflammation of these causes pain and dysfunction

Question 27

What happens to your joints as you age?

Answer 27

• The synovial fluid becomes more viscous which results in slower joint movements and reduced lubrication of joints
• Less water in your articular cartilage (in healthy individuals there is >75% water) which results in less shock absorption (loss of in-compressible water)
• So… less protection of articular surfaces and increased risk of damage!

Question 28

Sign of osteoarthritis in an affected joint

Answer 28

Uncontrolled addition of bone growth around the margins of the joint - jagged margin of the vertebrae