Human Gastrointestinal Surface pH Measured by Novel Electrode Systems

Rawlings, John Merritt (1987) Human Gastrointestinal Surface pH Measured by Novel Electrode Systems. MSc(R) thesis, University of Glasgow.

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Events occurring at the gastrointestinal mucosa have implications for the absorption of nutrients and the protection of the surface epithelium. In recent years, accumulating evidence suggests that the mucosal surface pH can differ from that of the bulk perfusing solution and that the surface pH is not necessarily the same in different areas of the alimentary tract. Measurements of surface pH have been performed by previous workers in animals both In vitro and in vivo and in human biopsy material. However, a comprehensive characterisation of gastro-duodenal mucosal surface pH in humans in vivo has yet to be published and no information exists at all about human in vivo jejunal mucosal pH. The purpose of this investigation was to measure gastrointestinal mucosal pH in humans in vivo and to compare results obtained from control patients and patients with gastrointestinal disease. Existing measuring systems of gastrointestinal pH are specifically designed to measure luminal pH or are unsuitable for mucosal pH measurements. Consequently, to measure mucosal pH in humans in vivo, two novel measuring systems were employed. To measure gastro-duodenal mucosal pH, an electrode was passed through the biopsy channel of an endoscope. Using this technique, the electrode could be seen to touch the mucosa in specifiable areas when measurements were made at endoscopy. Proximal intestinal mucosal pH was measured by attaching a plastic pH electrode to a Crosby biopsy capsule. When swallowed, the capsule-electrode assembly allowed for continuous measurement of intestinal mucosal pH and the retrieval of biopsy material for histological and biochemical analysis. A plastic pH electrode was required for use at jejunal biopsy because of the unsuitability of available glass electrodes. Two hydrogen ion-selective carriers were compared for their suitability as components in a plastic electrode for use in humans. The plastic pH electrodes were developed and constructed in the laboratory and the electrode properties were extensively characterised. The electrodes used at jejunal biopsy had comparable operational characteristics to glass pH electrodes within the physiological pH range. Measurements of jejunal mucosal pH were obtained in 9 control, 13 coeliac and 11 irritable bowel syndrome (IBS) patients. A pH gradient ranging from near neutral in the duodenum to an acidic pH of 5.9 in the jejunum was measured in control patients. In contrast, coeliac patients had a significantly alkaline pH in the duodenum and a jejunal mucosal pH of 6.7, significantly less acid than control values. Coeliac patients on a normal diet had a near neutral mucosal pH while that of patients on a gluten free diet was still significantly elevated. In IBS patients, jejunal mucosal pH was not significantly different from control values. An elevated jejunal mucosal pH in coeliac disease may result from a loss of acid secreting villous tip cells and neutral or alkaline secretion from the increased numbers of crypt cells associated with coeliac disease. There may also be a contribution from increased tissue permeability. Measurements of gastro-duodenal mucosal pH revealed that acid in the stomach had a significant influence on the recorded pH. Without gastric acid (pH>3), the mucosal pH was close to neutrality from the fundus to the duodenum in control patients. In contrast, in the presence of acid (pH<3), fundal and antral mucosal pHs were significantly more acidic than neutral. Duodenal pH was unaffected by the presence of acid in the stomach. In patients with gastric ulcer, the antral surface pH was near neutral in the absence of gastric acid and remained elevated even when acid was present. In gastric ulcer, a more alkaline antral surface pH was also associated with active ulceration but less so with healing ulcers and with gastritis without ulceration. Similarly, duodenal ulcer was associated with a strikingly alkaline duodenal mucosal pH. Once again, acid in the stomach accentuated the elevation in duodenal mucosal pH when compared with control values. It is proposed in the cytoprotection hypothesis that the mucosa can maintain a neutral surface pH in the presence of acid and that peptic ulcer patients have a reduced capacity to maintain this neutral layer. From the results obtained in this project, it is proposed that it is normal for acid to dissipate the "mucus-bicarbonate" layer and reduce mucosal pH. In addition, peptic ulceration is associated with alkalinity in the affected area and not a reduced mucosal pH as predicted. An hypothesis is presented which suggests that this alkalinity is inappropriate and may have pathological consequences for subsequent control of acid secretion, gastric emptying and pancreatic bicarbonate secretion.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Physiology
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-77487
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 09:07
Last Modified: 14 Jan 2020 09:07

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