A review of mixing and propulsion of chyme in the small intestine: fresh insights from new methods

Abstract

The small intestine is a convoluted flexible tube of inconstant form and capacity through which chyme is propelled and mixed by varying patterns of contraction. These inconstancies have prevented quantitative comparisons of the manner in which contractile activity engenders mixing of contained chyme. Recent quantitative work based on spatiotemporal mapping of intestinal contractions, macro- and micro-rheology, particle image velocimetry and real-time modelling has provided new insights into this process. Evidence indicates that the speeds and patterns of the various types of small intestinal contraction are insufficient to secure optimal mixing and enzymatic digestion over a minimal length of intestine. Hence particulate substrates and soluble nutrients become dispersed along the length of the lumen. Mixing within the lumen is not turbulent but results from localised folding and kneading of the contents by contractions but is augmented by the inconstant spatial disposition of the contractions and their component contractile processes. The latter include inconstancies in the sites of commencement and the directions of propagation of contraction in component groups of smooth muscle cells and in the coordination of the radial and circular components of smooth muscle contraction. Evidence suggests there is ongoing augmentation of mixing at the periphery of the lumen, during both the post-prandial and inter-meal periods, to promote flow around and between adjacent villi. This results largely from folding of the relatively inelastic mucosa during repeated radial and longitudinal muscular contraction, causing chyme to be displaced by periodic crowding and separation of the tips of the relatively rigid villi. Further, micro-rheological studies indicate that such peripheral mixing may extend to the apices of enterocytes owing to discontinuities in the mobile mucus layer that covers the ileal mucosa.

The DH31/CGRP enteroendocrine peptide triggers intestinal contractions favoring the elimination of opportunistic bacteria

“…Strikingly, we never observed the thickening of circular fibers, these latter being involved in normal peristalsis following food intake. Peristalsis corresponds to a wave of contractions of circular fibers associated with a relaxation of longitudinal fibers propagating along the length of the gut, leading to overall lengthening of the intestine [ 24 , 25 ]. Therefore, our results indicate that opportunistic bacteria rapidly provoke longitudinal visceral muscle contractions which do not correspond to peristalsis.…”

Effect of amino acid deficiency on precaecal amino acid digestibility in broiler chickens

“…A different lumen fill probably influenced the passage rate of the digesta through the gastrointestinal tract. Lentle and de Loubens () pointed out that there is evidence that contractile activity disperses the digesta along the length of the small intestine, and therefore, the lower amount of digesta per length of the small intestine facilitates mixing of the digesta by kneading and folding. For the present study, it appears possible that lower feed intakes resulted in lower amounts of digesta in the intestinal lumen and, consequently, increased mixing intensity within the small intestine.…”

The role of circular folds in mixing intensification in the small intestine: A numerical study

“…The segmentation, as opposed to peristalsis, was observed to be the main form of movement during the post-prandial period since residence time values should be longer than the time needed to achieve acceptable mixing (Husebye, 1999; Lentle and de Loubens, 2015; Sarna et al, 1983). The real-time motion of the intestinal tract can be illustrated using The ideally mixed state spatiotemporal maps (Lentle and de Loubens, 2015). Tremendous efforts have been made as well to characterize the physical and chemical properties of the gastrointestinal contents and intestinal structures.…”