The Role of Mucus Secretions in the Protection of the Gastrointestinal Mucosa

Abstract

The surfaces of all mucous membranes are protected by a layer of mucus. The protective value of this secretion lies not only in its characteristic physicochemical properties but also in the presence of certain specific constituents. It is a complex secretion, receiving contributions from many types of cell (Jones and Reid, 1978) in addition to material arising by transudation from plasma. Gastrointestinal mucus presents particular problems in this respect when attempts are made to define its nature and role because it is always admixed with copious secretions from sources other than the mucus-producing cell. These secretions, in particular sites, contain powerful proteolytic enzymes and glycosidases which are known to act upon mucus. Any material that survives into the colon is rapidly digested by the large numbers of bacteria that are present in that organ so that faeces contain little or no mucus in the healthy state. The gastrointestinal mucus layer is not likely to be radically different from that in other sites however. In that case, when first secreted, it is a complex secretion containing components arising by transudation (plasma proteins), from cell breakdown (DNA and lipids) or by active secretion (lysozyme, lactoferrin, secretory IgA and glycoprotein). A typical mucus secretion contains about 1% salt, 1% protein and between 1% and 3% glycoprotein (Creeth, 1978).