Gastrointestinal Mucus

  • A. Allen
  • N. Carroll
  • A. Garner
  • D. A. Hutton
  • C. W. Venables
Part of the NATO ASI Series book series (volume 80)


Mucus occurs throughout the gastrointestinal tract as a water insolublele gel adherent to the mucosal surface and as soluble or suspended mucus in the lumen. The principal function ascribed to mucus is protection of the underlying mucosa from the harmful factors in the lumen.1,2 In the stomach and duodenum the adherent gel together with the mucosal bicarbonate secretion provides an environment for neutralisation of luminal acid, maintaining a near neutral pH at the mucosal surface 3,4 (Fig. 1). Acid from the lumen readily diffuses through the mucus cover,6,7 but it is neutralised in the stable, unstirred layer within the mucus by bicarbonate secreted from the surface epithelial cells. In this way the adherent mucus gel limits the mixing of the bulk of luminal acid with the smaller quantity of mucosal bicarbonate secretion. Recent evidence for such a protective mechanism has come from studies of gastroduodenal epithelial bicarbonate secretion;4,8 the structure of mucus9,10 measurements of pH gradients adjacent to the mucosal surface11,12,13,14 and observations on the adherent mucus gel layer in situ.15,16 Although permeable to hydrogen and bicarbonate ions, mucus is not permeable to large molecular weight pepsins.10 A hydraulic pressure is created in the gastric glands and rapid secretion of H+ and pepsin will enable them to gain access to the stomach lumen through the thin cover of surface mucus. The annealing properties of mucus will allow it to reseal when secretion has ceased. Once in the lumen of the stomach, pepsin cannot diffuse back through the adherent gel and attack the underlying mucosal cells. Mucosal defence against pepsinolysis is further complicated by the fact that pepsin solubilises the mucus gel to produce soluble degraded mucus in the gastric juice.10,17,18 Therefore mucus will only provide an effective barrier against pepsin if proteolytic degradation at its luminal surface is balanced by secretion of new mucus gel.


Mucus Layer Unstirred Layer Gastric Mucus Mucosal Protection Peptic Ulcer Patient 
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Copyright information

© Plenum Press, New York 1984

Authors and Affiliations

  • A. Allen
    • 1
  • N. Carroll
    • 1
  • A. Garner
    • 3
  • D. A. Hutton
    • 1
  • C. W. Venables
    • 2
  1. 1.Department of Physiological SciencesUniversity of Newcastle upon TyneUK
  2. 2.Department of SurgeryUniversity of Newcastle upon TyneUK
  3. 3.Bioscience Department, I.C.I. Pharmaceuticals DivisionMacclesfield, CheshireUK

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