Ground substance

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Image:Chondroitin Sulfate Structure NTP.png

Ground substance is one of the three major components of the extracellular matrix (ECM) in connective tissue. ECM of connective tissue is made up of fibers, ground substance, and tissue fluid. Ground substance refers to components of the connective tissue that support and bind cells together and provide a medium for the exchange of materials, consisting of hyaluronic acid, chondroitin sulfate, dermatan sulfate, and keratan sulfate, proteoglycans and adhesion proteins.

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Ground substance is a dated term for extracellular matrix. Cells are surrounded by extracellular matrix in tissues, which acts as a support for the cells. Ground substance traditionally does not include collagen. Ground substance is the amorphous extracellular material in which the cells and fibers of connective tissue are embedded, also referred to as the extracellular matrix.

Ground substance is composed of plasma constituents, metabolites, water, ions and an assortment of large organic molecules, many of which are complex combinations of polysaccharides and proteins present between cells and fibers. The polysaccharides, collectively referred to as glycosaminoglycans (GAGs), include hyaluronic acid, which is more recently called hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, heparin, and heparen sulfate. Except for hyaluronic acid, the glycosaminoglycans are associated with proteins, and this combination is called proteoglycans. The proteoglycans, containing most of the interstitial fluid (about 11 L), are formed of a core protein, from which the glycosaminoglycans project like the bristles of a brush. With a strong affinity for holding water, proteoglycans are responsible for the gelatinous consistency of ground substance (extracellular matrix).

Also present in the ground substance are glycoproteins, so-called adhesion proteins that are responsible for linking components to one another and to the surface of cells. Most abundant is the adhesion protein fibronectin, which links ground substance and collagen fibers together.

Ground substance can be fluid, semifluid, gelatinous, or calcified. It supports cells, binds them together, stores water via glycosaminoglycans, and provides a medium through which substances are exchanged between blood and cells. As such, ground substance plays an active role in how tissues develop, migrate, proliferate, change shape, and carry out their metabolic functions.