Synovial fluid is produced through a filtration process and cellular secretion. It's essentially derived from two main sources.
Formation of Synovial Fluid
Synovial fluid is formed through a combination of:
- Ultrafiltration of Blood Plasma: Synovial fluid begins as an ultrafiltrate of blood plasma [1]. This means that blood plasma is filtered, and smaller molecules pass through into the joint cavity while larger components like cells and large proteins are retained in the bloodstream.
- Secretion by Synovial Cells: Fibroblast-like type B synovial cells actively secrete essential components into the filtered plasma to complete the synovial fluid composition [1].
Composition of Synovial Fluid
The resulting synovial fluid contains key components that contribute to its function:
| Component | Source | Function |
|---|---|---|
| Hyaluronan | Secreted by Synovial Cells | Provides viscosity and lubrication; helps reduce friction in the joint. |
| Lubricin | Secreted by Synovial Cells | Essential for boundary lubrication, reducing wear and tear between cartilage surfaces. |
| Proteinases | Secreted by Synovial Cells | Enzymes involved in maintaining tissue homeostasis and remodeling in the joint. |
| Collagenases | Secreted by Synovial Cells | Enzymes that degrade collagen; contribute to tissue turnover and remodeling within the joint. |
| Prostaglandins | Secreted by Synovial Cells | Lipid compounds involved in inflammation and pain signaling. |
| Other Proteins | From Ultrafiltrate & Secreted by Synovial Cells | Various proteins from plasma and secreted by cells contribute to fluid properties and joint health |
Summary
In essence, synovial fluid is produced by the following:
- Blood plasma is filtered (ultrafiltrated) into the joint space.
- Fibroblast-like type B synovial cells secrete specific substances like hyaluronan, lubricin, proteinases, collagenases, and prostaglandins to enrich the fluid.
This combined process creates the viscous and lubricating fluid critical for joint health and function.
