|ExtraCELLULAR MATRIX... (ECM)
ECM… is extracellular space filled with a network of macromolecules (polysaccharides & proteins) secreted by a cell. The ECM molecules are secreted by cells called fibroblasts. The ECM occurs in all tissues, even blood (plasma is the matrix). It serves as a scaffold or support for cells and some cellular functions. The ECM is made of polysaccharides (glycosaminoglycans) linked to proteins (proteoglycans) and fibrous proteins including collagen & elastin and adhesive proteins, like fibronectin (a dimer composed of two lagre subunits joined by a pair of S-S- bonds) & laminin. A major component of ECM's is hyaluronic acid, a large polysaccharide made of glucuronic acid & glucosamine that attracts water can serve as a lubricant in joint fluid.
Proteoglycans retain water forming a hydrated-gel substance with embedded fibers through which ions, hormones & nutrients can freely move. Collagen (with long, stiff, helical structures) gives the ECM strength; elastins give it resilience; & fibronectins help fibroblast & other cells attach to the ECM (fibronectin domains binds to collagen & heparin and to specific integrins on the surfaces of various types of cells). Laminin promotes attachment of epithelial cells to the basal lamina and integrins.