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CONNECTIVE TISSUE (I) PROPER Roger J. Bick Reading: Gartner & Hiatt, Chapter 3; Klein and McKenzie, p77-93 Objectives: List components of ground substance. List major fiber types found in connective tissue matrix. List 5 types of collagen and their respective distributions. Identify the cell types of connective tissue proper, their origins, and major functions. Recognize and classify 3 types of adult connective tissue proper. Review the composition of the basement membrane. Key Words: Mesenchyme, fibroblast, macrophage, Kupffer cell, plasma cell, eosinophil, mast cell, collagen, ground substance, basement membrane I. COMPOSITION OF CONNECTIVE TISSUE A. Composed of cells embedded in an extracellular matrix (ECM) 1. Composed of ground substance, fibers, and tissue fluid. 2. The variation in the cells and components of the ECM is responsible for the different types of connective tissue throughout the body. B. Functions in a wide variety of supportive and protective roles. II. GROUND SUBSTANCE A. A colorless, transparent mixture of proteins found between the cells and fibers of connective tissue. 1. High viscosity contributes to its role as a lubricant and a physical barrier to penetration by bacteria. 2. Composed of glycosaminoglycans (GAGs), proteoglycans, and glycoproteins. A. Glycosaminoglycans 1. Long, non-branched polysaccharide chains consisting of repeating disaccharide units. All are sulfated, except hyaluronic acid, and have a strong negative charge. 2. Hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate.
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B. Proteoglycans 1. All GAGs, except those composed of hyaluronic acid, can be covalently bound to a protein core to form proteoglycans . Molecules are 80-90% carbohydrate and attract water to form a gel. 2. In addition to giving support to the connective tissue matrix, they act as binding sites for growth factors and signaling molecules. D. Glycoproteins also contain a protein core and carbohydrates, however the protein component predominates and the carbohydrate moiety is branched rather than linear. 1. Function in the adhesion of cells to each other and to the fibers of the extracellular matrix a. Fibronectin is made by fibroblasts and mediates normal cell adhesion and migration. b. Laminin is made by epithelial cells and mediates adhesion of these cells to the underlying basement membrane. 2. Integrins – transmembrane proteins on cells that serve as receptor sites for the glycoproteins. One end binds to proteins in the ECM; the other end attaches to actin microfilaments within the cell. This process is mediated by intracellular proteins ( paxilin, vinculin, talin ). III.
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