Synovium & Synovial Fluid Usama Tariq G10 INTRODUCTION The synovial membrane is soft and thin membrane yet has various significant roles that are very essentials for our body movements. • Synovium is a specialized connective soft-tissue membrane that lines the inner surface of synovial joint capsules. • Together with bone articular cartilage, tendon, ligament, and fibrous capsule, it is an important component of the tissues that form an integrated joint • Synovial fluid lubricates articular cartilage and provides nourishment through diffusion. It made from a ultrafiltrate of blood plasma, produced and regulated by the synovium. ANATOMY The synovium is vascularized, unlike the avascular articular cartilage (the other inner joint cavity surface tissue). Therefore, it serves as an important communication channel for transport of nutrients, debris and waste removal, immune modulation, and inflammation in the joint. These specialized functions are achieved by major cell types in synovial membrane, both resident and infiltrated. The membrane consists of 2 layers: Synovial membrane showing the fibrous and the intimal layer. ANATOMY 1) Intimal layer: Well innervated and vascularized containing different types of cells eg fibroblasts type cells, macrophages, adipocytes, nerve fibers, vascular endothelial cells, lymphocytes. Responsible for: production of synovial fluid components; absorption from the joint cavity; blood/synovial fluid exchanges. Features two types of synoviocytes: • Type A - macrophage-like cells are derived from hematopoietic monocyte lineage. • Type B cells - fibroblast-like, responsible for synthesizing and secreting major extracellular matrix proteins in synovial fluid including hyaluronic acid and lubricin. ANATOMY 2) Subintima layer • Thicker layer of loose connective tissue which contains fewer cells • Composed of fatty, fibrous or loose areolar tissue. SYNOVIAL FLUID This fluid is generated from an ultrafiltrate of blood plasma which is regulated by synovium. The purpose of this fluid is to lubricate the cartilage of the bone joint and provide nourishment through diffusion. It is made from a ultrafiltrate of blood plasma and is regulated by the synovium. E.g. healthy knee contains ~2mL of synovial fluid Consists of: • Hyaluronic acid: a viscous glycosaminoglycan serves as a structural element and lubricant. • Lubricin: the most lubricating and anti-adhesive molecule in the human body. • Proteinase: an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids. • Collagenases: enzymes that break the peptide bonds in collagen. • Prostaglandins: produced in nearly all cells and are part of the body's way of dealing with injury and illness. SYNOVIAL FLUID Biomechanics: • Synovial fluid exhibits non-Newtonian flow characteristics i.e Viscosity coefficient is not a constant; Fluid is not linearly viscous; Viscosity increases as the shear rate decrease. In case of joint inflammation, swelling or redness, a synovial fluid analysis may be done. This sample is used to detect any traces of lactic dehydrogenase, uric acid, and protein which can be held responsible for inflammation
