Joints, synovial fluid and cartilage Flashcards
Where do you find fibrous joints?
- Sutures in the skull
- Peridontal ligament - anchors each tooth to the jaw
- Interosseous membranes - found between bones
Name the 2 different types of cartilaginous joints
- Primary cartilaginous joint or Synchondrosis
- Secondary cartilaginous joint or Symphysis
Synchondrosis/primary c. joint
- Contains 1 type of cartilage = hyaline
- Found in growing long bones
Symphysis / secondary c. joint
- Contains 2 types of cartilage = hyaline and fibrocartilage
- Found between vertebrae
What is the most mobile type of joint?
Synovial
Describe a synovial joint
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
What types of things stabilise a joint? (3)
The shape of the articulating surfaces
Capsules and ligaments surrounding the joint - want these to be strong
Muscles
Mechanically which is stronger, hyaline cartilage or fibrocartilage?
Fibrocartilage
What are the 2 different layers in articular cartilage called?
- Superficial layer
- Transitional layer
Describe the Superficial/tangential layer
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
Describe the Transitional layer
Round chondrocytes that produce proteoglycans such as aggrecan (good at binding to water)
What is a proteoglycan?
- 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!
What is a Glycoprotein?
Proteins to which oligosaccharide chains are attached, i.e. more a protein than a carbohydrate!
What is a Glycosaminoglycans or GAGs?
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
Average cartilage thickness around the body
- 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
What produces synovial fluid?
Synovial membrane (synovium)
- Synoviocytes within the synovium produce the fluid
3 A’s of cartilage
- Avascular
- Aneural
- Alymphatic
What type of tissue makes up synovial fluid?
Synovium
Type A synoviocyte
- Remove debris/waste
- Look like macrophages
- Contribute to synovial fluid production but not main producers
Type B synoviocyte
Main producer of synovial fluid
- Fibroblast-like cells
Functions of synovial fluid
- Nutrition of cartilage (articular c., menisci/discs)
- Removal of waste products
- Lubrication => less friction => less wear
What is the simplest way of lubricating the articular surface?
Boundary Glycoproteins such as lubricin bind to receptors on articular surfaces to form a thin film
3 mechanisms of lubrication of joints
- Boundary
- Hydrodynamic
- Weeping
These work together in a healthy joint to lubricate it nicely
Hydrodynamic (Like aquaplaning)
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
Weeping lubrications
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
What are Bursae?
- 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
What happens to your joints as you age?
- 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!
Sign of osteoarthritis in an affected joint
Uncontrolled addition of bone growth around the margins of the joint - jagged margin of the vertebrae
