Primary Components of Synovial Fluid
Synovial fluid is a viscous, clear or pale-yellow liquid found in the joint cavity. It is secreted by the synovial membrane and serves lubrication, shock absorption, nutrient transport, and waste removal functions. Here are its key components
1. Hyaluronic Acid (HA)
- Hyaluronic Acid (HA)
- Function: Gives synovial fluid its viscosity and elasticity, enabling lubrication and cushioning during joint movement.
2. Lubricin
- Source: Produced by chondrocytes and synoviocytes.
- Function: Coats cartilage surfaces to reduce friction during movement
3. Electrolytes and Small Molecules
- Examples: Sodium, potassium, chloride, bicarbonate, calcium, glucose, and urea.
- Function: Maintain osmotic balance and metabolic activity within the joint.
Note: Glucose is typically at a level similar to plasma but may drop in inflamed joints (e.g., in RA)
4. Amino Acids and Nutrients
- Function: Provide building blocks for cartilage maintenance and cellular functions within the joint.
5. Enzymes
- Examples: Matrix metalloproteinases (MMPs), hyaluronidase, collagenase.
- Function: Involved in normal remodelling; overactive in inflammation, leading to cartilage degradation.
6. Cytokines and Growth Factors
- Normal joints: Low or undetectable.
- In pathology: Elevated levels of IL-1β, TNF-α, IL-6, VEGF, etc. contribute to inflammation and joint damage.