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Additional recommended knowledge
The inner membrane of synovial joints is called the synovial membrane, which secretes synovial fluid into the joint cavity. This fluid forms a thin layer (approximately 50 micrometres) at the surface of cartilage, but also seeps into microcavities and irregularities in the articular cartilage surface, filling any empty space . The fluid within articular cartilage effectively serves as a synovial fluid reserve. During normal movements, the synovial fluid held within the cartilage is squeezed out mechanically (so-called weeping lubrication) to maintain a layer of fluid on the cartilage surface.
Normal synovial fluid contains 3-4 mg/ml hyaluronan (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetylglucosamine joined by alternating beta-1,4 and beta-1,3 glycosidic bonds . Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and lubricate the surfaces between synovium and cartilage.
Synovial fluid also contains lubricin secreted by synovial cells. It is chiefly responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage. There is also some evidence that it helps regulate synovial cell growth.
Health and disease
Synovial fluid can be collected by syringe in a procedure termed arthrocentesis, also known as joint aspiration.
Synovial fluid can be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic:
When two parts forming a joint are pulled away from each other, the joint capsule increases in volume but the synovial fluid in the capsule no longer fills it all. Gases dissolved in the fluid quickly fill the empty space causing a sharp cracking sound. . The general term for this is cavitation.
External links and references
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Synovial_fluid". A list of authors is available in Wikipedia.|