Disease Seminar Handbook W12

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Unformatted text preview:  63. Pay particular attention to pages 57 ­60. By no means are you expected to memorize everything in the chapter, but you will likely find it to be a great resource for definitions and figures to help orient yourself when reading more complex discussions of OA. As you likely have come across, a joint is the location where two or more bones come together, such as the hip or knee. The bones of a joint are covered by a smooth and spongy material called cartilage. Cartilage allows the joint to move smoothly, without pain. In addition, the joint is lined by synovium; a thin layer of tissue which produces a slippery fluid called synovial fluid that nourishes the joint and helps reduce friction. Ligaments are strong bands of tissue that connect the bones and stabilize the joint in addition to muscles and tendons to enable movement (Fig.1) 21 Figure 1. The Normal Joint. Courtesy of Arthritis Ireland. Cartilage is composed of chondrocytes and an extracellular matrix of water, collagen, proteoglycans, in addition to other components such as adhesives and lipids. Cartilage is sub ­ divided into several different types: hyaline, elastic, and fibrocartilage. Please refer to your textbook in the assigned reading pages (above) for a description of each of these types of cartilage! Unlike other connective tissues, cartilage does not contain blood vessels. Because of this, it heals very slowly. Composition of hyaline cartilage Chondrocytes: Chondrocytes are important in the control of matrix turnover through production of: collagen, proteoglycans, and enzymes for cartilage metabolism. Matrix: Water distribution varies, making up 65% of wet weight at the deep zone and 80% at the surface. Weight bearing capacity is made possible through regional changes in water content which allow deformation of the cartilage surface in response to stress. The matrix also provides nutrition and lubrication of cartilage. Proteoglycans: Proteoglycans provide compressive strength and regulate matrix hydration by providing a porous structure to trap and hold water. Proteoglycans are composed of subunits of glycosaminoglycans (GAG’s - disaccharide polymers): chondroitin-4-sulfate (decreases with age), chondroitin-6-sulfate, keratin sulfate (increases with age). GAG’s are bound to a protein core by sugar bonds to form a proteoglycan aggrecan molecule. Aggrecan molecules are further stabilized by link proteins which bind them to hyaluronic acid to form a proteoglycan aggregate (Fig. 2). 22 Figure 2: Proteoglycan aggregate. Courtesy of World Ortho. Adhesives: Adhesives that mediate the molecular interactions between chondrocytes and collagen fibrils are fibronectin, chondronectin and anchorin CII. Lipids are present in cartilage but their function is unknow...
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