ABSTRACT
The extracellular matrix (ECM) constitutes a significant part of the multicellular animal organism. Except blood, there are no tissues without an ECM. In connective tissue the matrix is abundant, while its bulk is much less in other tissues where sometimes special techniques are needed for its detection. The matrix molecules are produced and degraded by cells. Multicellular animals can function only because single cells learned to synthesize, and maintain macromolecular connections between them, and they have become dependent upon the matrix they made. Collagen is the most ubiquitous protein in animal kingdom. Proteoglycans contain a protein core to which sulfated glycosarninoglycans are bound covalently. The elastic behavior of some tissues is mainly due to the presence of elastic fibers in the ECM. The morphological appearance of elastic fibers is simple; the mature fibers appear as homogeneous structures under electron microscope. They have been considered to possess an amorphous structure. Polarization microscopy revealed that elastic fibers have submicroscopically oriented constituents.
