Synovium Function mediates nutrient exchange between blood and joint fluid Composition vascularized connective tissue is porous and lacks basement membrane cell types type A cells derived from macrophages non-fixed cells with antigen presenting ability located in superficial layer important in phagocytosis type B cells fibroblast like cells rich rough endoplasmic reticulum and dendritic processes that reach out to the joint surface located at various depths, frequently in deeper layer produce synovial fluid produce hyaluronic acid, fibronectin, collagen type C cells intermediate cell type unknown function and origin may serve as multi-potent precursor to either type A or B synovial cells Synovial Fluid Function lubricates articular cartilage and provides nourishment through diffusion Origin made from a ultrafiltrate of blood plasma regulated by synovium healthy knee contains ~2mL of synovial fluid Consists of hyaluronin uridine diphosphoglucose dehydrogenase enzyme critical for its synthesis lubricin a key lubricating glycoprotein reduces coefficient of friction within the joint proteinase urokinase-type plasminogen activator activates plasmin and prevents intra-articular clot formation collagenases prostaglandins Biomechanics synovial fluid exhibits non-Newtonian flow characteristics the viscosity coefficient is not a constant the fluid is not linearly viscous viscosity increases as the shear rate decreases