Other Mucus Components

When considering the influence of mesh size it is important to recognize the effect of other mucus components (see below) and also that the GI mucus appears to comprise two continuous but distinct layers the outer, loosely adherent mucous layer and the inner, firmly adherent mucus layer (Atuma et al. 2001). These mucus layers differ in thickness (Table 2.2) and perhaps organization (pore mesh), although the underlying reason for this intramucus compartmentalization has not yet been determined. The fact that the inner mucus layer is most abundant and the ratio of inner layer/ outer layer thickness is larger in the stomach supports the view that the former has a protective function while the latter would mainly function as a lubricant (Atuma et al. 2001). 

Clues to other signals for attachment and invasion of the host by helminth parasites have come from work on fish parasites such as Acanthostomum brauni. Cercariae of A. brauni do not recognize small molecules such as amino acids, monosaccharides or electrolytes, but do respond to hyaluronic acid and glycoproteins for attachment (34). Penetration of the host is triggered by free fatty acids and mucus components present on the fish skin surface (35). 

Mucolytics reduce the viscosity of tenacious and purulent mucus, thus faciUtating removal. The distinction between mucolytics and other classes of expectorants is frequently blurred. Steam, sometimes in conjunction with surfactants or volatile oils, has long been used to decrease viscosity by physical hydration. However, agents that chemically depolymerize certain components of mucus are available. Trypsin and other proteolytic enzymes have shown good clinical activity because of their abiUty to cleave glycoproteins. Pancreatic domase, which depolymerizes DNA found in purulent mucus, also has shown clinical utihty. 

Mucus is basically a semi-dilute aqueous solution in which very long, highly hydrophilic and flexible mucin macromolecules form a tri-dimensional network or gel that keeps the water molecules and other components together. Mucins... 

Similar inferences were drawn regarding dissolved mucin from dog stomach by Grossberg et al. (G70), who determined hexosamine and lu-onic acid contents of canine gastric juice and mucus before and after histamine and sham feeding. Determinations were performed after acid hydrolysis and showed marked variations in the mutual ratio of these two components, depending on the nature of the stimuli applied. This suggested the existence of at least two different kinds of mucoprotein in these secretions—one containing uronic acid, and the other hexosamine with or without small amounts of the former (Fig. 17). 

Native mucus secretions normally contain 1% of salts and other dialyz-able components, 0.5 -1 % of proteins, a similar proportion of carbohydrate-... 

Bacteria causing gastrointestinal infection need to penetrate the mucus layer before attaching themselves to the epithelial surface. This attachment is usually mediated by bacterial fimbriae or pilus structures, although other cell surface components may also take part in the process. Adherent bacteria colonize intestinal epithelium by multiplication and initiation of a series of biochemical reactions inside the target cell through signal transduction mechanisms (with or without the help of toxins) (51). 

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