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Transcript
Today: The extracellular matrix (ECM) Tissues & cells are surrounded by EXTRACELLULAR MATRIX Extracellular matrix: ground substance, fibers And water Ground substance: -glycosamino glycans -proteoglycans -adhesive glycoproteins Functions of ground substance: -resist compression -retard movement of bacteria and metastatic cells -filtration barrier for diffusable signaling factors -binding site for contact signaling factors Glycosaminoglycans Sulfated - chondroitin-4-sulfate, keratin sulfate, Heparin sulfate, heparin Not sulfated - Hyaluronic acid -long unbranched polysaccharides -repeating disaccharide units, the amino sugar N-actylglucosamine and uronic acid Glycosaminoglycans -long unbranched polysaccharides -repeating disaccharide units -the amino sugar N-actylglucosamine and uronic acid Sulfated sugars attract carboxyl groups (neg charged), these bind onto to Na, attracts water resists compression Proteoglycans -sulfated glycoamino glycans and a protein core -cover huge areas of extracellular matrix - eg. Aggrecan in cartilage and other connective tissues -contains hyaluronic acid + link protein + core protein Collagen attaches to the proteoglycans Pathogenic bacteria (S. aureus) secrete hyaluronidase, --> destroys extracellular matrix Adhesive Glycoproteins Cells can adhere to the ECM molecules Adhesive glycoproteins bind to integrins surface proteins eg. Of glycoproteins -fibronectin -laminin -tenascin Fibronectin is on fibroblasts. -has binding sites for hyaluronic acid and other glycosaminoglycans -has binding sites for collagen (an extracellular fibrous protein) -has amino acid sequences for binding onto the cell membrane (arg, gly, asp) -anchors fibroblasts to the ECM -marks migratory pathways for progenitors Extracellular protein fibers: Collagen fibers Elastic fibers Reticular fibers ______________________ Collagen is very tough and fibrous Collagen is very tough and fibrous, how? • Fibers fibrils made of tropocollagen molecules. • 3 polypeptide chains, triple helix • many H bonds across chains Collagen is very tough -has strong tensile forces -makes up about 20% of the body -with H & E stain, appear pink (acidophilic) -no color if not stained -each collagen fiber is 10 mm wide Collagen • At least 15 types of collagen • Type I – coarse thick filaments, Ct dentin • Type II – fine fibers, hyaline and elastic cartilage • Type III – reticular, glycosylated • Type IV – BM, not fibrillar