Synovial fluid is the clear, viscous fluid secreted by the membranes in tendon sheaths and joint cavities. It functions as a lubricant between articulating joints, which reduces friction during movement. Synovial fluid is considered a shear thickening fluid because it increases in viscosity under applied pressure. The increase in viscosity provides shock absorption, which protects the joints.
In Our Own Words
Synovial joints are a type of movable joint in the body, such as the elbow and knee. Inside the joint is a membrane, which secretes synovial fluid. The thick fluid lubricates the joint, which allows it to move more easily and also reduces friction. The thickness of synovial fluid also increases when pressure or force is applied to the joints. The increase in thickness cushions the joint and provides shock absorption. Joint fluid, when drawn out with a syringe and analyzed, sometimes offers diagnostic information; and certain medications can be injected into the joint fluid.