| Popis: |
Summary Extracellular matrix (ECM) surrounds the cells in tissues. It contains glycosami-noglycans (GAGs) which attract the water that is its major component. Most GAGs are covalently linked to the protein core of a proteoglycan (PG). There are at least 16 genetically distinct types of collagen in ECM; over 70% of the collagen consists of types I, II and III which form fibrils. Collagen fibrils provide tensile reinforcing in ECM. ECM also contains elastic fibers, glycoproteins, cytokines, growth factors, and enzymes which are capable of degrading the matrix. Molecules like fibronectin are capable of binding cells to the macromolecular components of ECM. Receptors enable the cell surface to interact with these macromolecules. Integrins provide an important example of these receptor molecules which extend into the plasma membrane. The binding affinity to ECM can then be regulated from within the cell (inside-to-out signalling) and the matrix can influence events within the cell (outside-to-in signalling), including differentation. Thus, ECM can influence development at the cellular level as well as forming the structures of the body. Changes in the ECM occur during aging but it may be difficult to distinguish aging from degeneration. Pathological changes involve an alteration in the normal matrix or synthesis of abnormal matrix; alteration in normal matrix usually involves an increase or a decrease in the amount of matrix which retains its normal composition. |
