Physiology of Joints Flashcards
1111+What 2 main functions do joints provide for MSK system?
- Structural support
- Purposeful movement
What 3 ways do joints help provide purposeful movement?
- Stress distribution
- Confer stability - shape of articular component, ligaments, synovial fluid (acts as an adhesive seal)
- Joint lubrication- cartilage interstitial fluid, synovium-derived hyaluronic acid (mucin - polymer of dissacharides), synovium-derived lubricin (glycoprotein)
What type of bones have synovial joints?
Diarthrosis: articulation that permits free movement
What type of bones have fibrous joints?
Synarthrosis: bones united by fibrous tissue, doesn’t usually allow any movement
- Examples are the bones of the skull in adults
What types of bones have cartilaginous joints?
Amphiarthrosis: bones united by cartilage, allow limited movement
- Examples are the IV discs, pubic symphysis, part of the sacroiliac joints, costochondral joins
What are bones separated and united by?
-Separated by a cavity (containing synovial fluid)
-United by a capsule (and other extra-articular structures e.g. ligaments, tendons and bursae)
What is the synovial membrane?
A vascular connective tissue with capillary networks and lymphatics which lines the inner aspect of the fibrous capsule (about 60 µm thick in the human knee)
What does the synovial membrane contain?
Synovial cells (fibroblasts) which produces the synovial fluid (about volume <3.5 m)
What is the joint capsule and what does it contain?
-It isolates and covers the entire joint. -Contains an outer fibrous layer and an inner layer known as the synovial membrane.
What are the articular surfaces of bones covered with?
Cartilage
What is a simple synovial joint? Example
One pair of articular surfaces
-Metacarpophalangeal joint
What is a compound synovial joint? Example
More than one pair of articular surfaces
-Elbow joint
Describe characteristics synovial fluid in join cavity (3)
-Continuously replenished by the synovial membrane
-High viscosity - mainly due to the presence of hyaluronic acid (mucin) produced by the synovial cells
-The viscosity and elasticity of the synovial fluid varies with joint movement (Rapid movement is associated with decreased viscosity and increased elasticity)
Is there uric acid present in synovial fluid?
Yes, derived by dialysis of blood plasma
What is usual colour of synovial fluid and when does it turn red?
-Clear and colourless
-Turns red in traumatic synovial tap and in haemorrhagic arthritis
Name 5 functions of synovial fluid
- Lubricates joint
- Facilitates joint movement - reduces friction
- Helps minimise wear-and-tear of joints through efficient lubrication
- Aids in the nutrition of articular chondrocytes
- Supplies the chondrocytes with O2 and nutrients and removes CO2 and waste products (articular cartilage is avascular)
Name 3 functions of articular cartilage
- Provides a low friction lubricated gliding surface which helps prevent wear-and-tear of joints
- Distributes contact pressure to subchondral bone
- The fluid and solid phase of the cartilage plays a significant role in determining the mechanical properties of cartilage
Describe structure of articular cartillage
- The articular cartilage is usually hyaline
- It is elastic and has sponge-like property
-The zones differ in organisation of collagen fibres and relative content of cartilage components
Describe the constituents of the ECM
-Water (70%) - maintains the resiliency of the tissue and contributes to the nutrition and lubrication system
-Collagen (20%) - mainly type II (elastic)
-Proteoglycans (10%) - responsible for the compressive properties associated with load bearing (act like ‘balloons’)
What is the ECM synthesised by?
-Synthesized, organised and degraded by chondrocytes
Is articular cartilage avascular?
True
Where do chondrocytes receive their nutrients from?
Chondrocytes receive nutrients and O2 via the synovial fluid
How can joint disease interrupt the normal cycle of joint reparation?
-In normal joints, the rate of ECM degradation doesn’t exceed the rate at which it is replaced
- Joint disease can occur if the rate of ECM degradation exceeds the rate of its synthesis
Why does articular cartilage have poor healing/repair?
It is avascular
What 4 things tend to go wrong in joint disease?
- Cartilage and synovial fluid decomposition and function deteriorate with age and repeated wear and tear → osteoarthritis
- Synovial fluid proliferation and inflammation → rheumatoid arthritis
- Deposition of salt crystals e.g. uric acid → gouty arthritis
- Injury and inflammation to periarticular structures can cause soft tissue rheumatism e.g. injury to the tendon causes tendonitis
