Synovial fluid exists as what in the joint capsule?

• A. Lubricant and nutritional fluid
• B. Waste product
• C. Immune cell reservoir
• D. Blood plasma

Answer: (A)

Synovial fluid’s main role in the joint capsule is to act as a lubricant and a source of nutrients for the cartilage. It creates a slippery film between articulating surfaces, greatly reducing friction during movement, and its viscous, hyaluronic-acid–rich composition helps cushion and distribute loads. It also serves as a medium through which nutrients diffuse to avascular articular cartilage and wastes are removed. The fluid is produced by the synovial lining and is an ultrafiltrate of plasma that has been modified; it is not simply waste, nor is it a reservoir of immune cells or just blood plasma. In health, this combination of lubrication and nourishment best explains its presence in the joint.