Luminal mucosal surface

At pH 4 most bacteria are killed within 30 min, and at physiological luminal pH, 99% of bacteria are killed within 5 min [14], Certain bacteria, like lactobacilli, are more acid-resistant, and some microbes survive the hostile gastric environment by colonizing luminal niches at the mucosal surface, protected by gastric bicarbonate secretion. This is the case for Helicobacter pylori, related spiral-... 

In addition to the longitudinal pH gradient, there is a pH gradient starting with the lumen to the absorbing surface [109,110]. Because of this gradient, the pH at the mucosal surface of the small intestine is different from that of the luminal content (a decrease of at least 1 pH unit, e.g., from 7.1 to 6.1) [111,112]. It was shown that the acidic microclimate is an essential determinant in fatty acid uptake after micellization [113]. The presence of a low-pH compartment facilitates the dissociation of mixed micelles made up of taurocholate and oleic acid. The rate of fatty acid diffusion in the mucin layer was estimated to be 400% of that in a buffer solution [114]. 

The gastrointestinal (GI) microflora plays an important role in the health status of people and animals. The GI tract represents a much larger contact area with the environment, compared to the 2 m2 skin surface of our body (van Dijk 1997). The mucosal surface of the small intestine is increased by forming folds, intestinal villi, and the formation of microvilli in the enterocyte resorptive luminal membrane. The resulting surface of GI system is calculated to be 150-200m2, therefore it provides enough space for the interactions related to digestion and for the adhesion to the mucosal wall. 

Q1 The mucosa is a mucous membrane which forms the innermost layer of the intestine. In the small intestine the mucosal surface area is increased greatly by folds and by villi, finger-like projections containing a core with a lymph capillary (lacteal) and blood vessels. Villi are covered by absorptive columnar epithelial cells whose luminal surface is further increased by microvilli (brush border) on which digestive enzymes and transport mechanisms for inorganic ions are located. 

In the toad urinary bladder, an experimental model of the mammalian collecting tubule, addition of hthium to the mucosal surface (but not to the serosal surface) markedly inhibited both basal and arginine vasopressin-stimulated water flow [50]. The concentration of mucosal lithium used in these studies (10 mEq/L) was comparable to or even lower than that usually found in the urine of patients on well-controlled lithium therapy (that is, 10 to 40 mEq/L) [63] Fernandez et al. [53] confirmed the inhibitory effect of lithium on water flow in toad urinary bladders exposed only submaximal concentrations of arginine vasopressin. Inhibition of cyclic adenosine monophosphate-stimulated water flow when lithium (2 mEq/L) was applied to the serosal surface of the toad bladder was reported in one study. Such an effect of lithium, when applied to the serosal surface has, to our knowledge, not been found by any other investigators. As herein discussed, the bulk of evidence supports the notion that the action of lithium on water transport is the result of its cell uptake from the luminal (apical) surface of the collecting tubule. 

Flemstroem, G. and Kivilaakso, E. (1983). Demonstration of a pH gradient at the luminal surface of rat duodenum in vivo and its dependence on mucosal alkaline secretion, Gastroenterology, 84, 787-794. 

The IF-cobalamin complex binds to specific receptors on the luminal surface of ileal mucosal cells. Binding requires Ca + and occurs optimally at pH >6.6. IF may enter the mucosal cell with cobalamin, or it may bind to the receptor and release the vitamin into the cell interior. The IF-receptor complex may then remain on the cell membrane and transport other molecules of cobalamin into the cell. 

The luminal surface of the GIT is covered by mucosal cells that produce mucus to protect the mucosa from acids and harmful luminal conditions and secretes digestive enzymes and regulatory peptides specific to each section of the GIT (Hall 2011). Half of the GIT fluid is secreted by the salivary glands, pancreas, and liver. The stomach mucosa contains different types of cells with distinct... 

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