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Annals of the New York Academy of Sciences (1)
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences (1)
Proceedings of the Royal Society B: Biological Sciences (1)
Brasseur, James G. (2)
Abrahamsson, Bertil (1)
Ailiani, Amit C. (1)
Banco, Gino G. (1)
Brasseur, James G (1)
Braverman, Alan S. (1)
Fried, Michael (1)
Indireshkumar, Keshavamurthy (1)
Miller, Larry S. (1)
Neuberger, Thomas (1)
Pal, Anupam (1)
Ruggieri, Michael R. (1)
Schwizer, Werner (1)
Vegesna, Anil K. (1)
Wang, Yanxing (1)
Webb, Andrew G. (1)
Year of Publication
The esophagogastric junction
Miller, Larry S.
Vegesna, Anil K.
Braverman, Alan S.
Ruggieri, Michael R.
Annals of the New York Academy of Sciences
The following discussion of the esophagogastric junctions includes commentaries on the three component structures of the sphincteric segment between the stomach and the esophagus; the pressure contributions from the three sphincteric components in normal subjects and in gastroesophageal reflux (GERD) patients; the mechanism of action of endoscopic plication to determine the underlying pathophysiology of GERD; and in vitro muscle strip studies of defects within the gastroesophageal sphincteric segment potentially leading to GERD.
clasp muscle fibers; sling muscle fibers; gastroesophageal junction; lower esophageal sphincter; upper gastric sphincter defects in GERD; missing sphincter; Endocinch; muscarinic receptors; in vitro muscle strips; stretch-induced tone; nicotine-induced relaxations
A multiscale lattice Boltzmann model of macro- to micro-scale transport, with applications to gut function
Banco, Gino G.
Webb, Andrew G.
Ailiani, Amit C.
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
Nutrient absorption in the small intestine cannot occur until molecules are presented to the epithelial cells that line intestinal villi, finger-like protrusions under enteric control. Using a two-dimensional multiscale lattice Boltzmann model of a lid-driven cavity flow with ‘villi’ at the lower surface, we analyse the hypothesis that muscle-induced oscillatory motions of the villi generate a controlled ‘micro-mixing layer’ (MML) that couples with the macro-scale flow to enhance absorption. Nutrient molecules are modelled as passive scalar concentrations at high Schmidt number. Molecular concentration supplied at the cavity lid is advected to the lower surface by a lid-driven macro-scale eddy. We find that micro-scale eddying motions enhance the macro-scale advective flux by creating an MML that couples with the macro-scale flow to increase absorption rate. We show that the MML is modulated by its interactions with the outer flow through a diffusion-dominated layer that separates advection-dominated macro-scale and micro-scale mixed layers. The structure and strength of the MML is sensitive to villus length and oscillation frequency. Our model suggests that the classical explanation for the existence of villi—increased absorptive surface area—is probably incorrect. The model provides support for the potential importance of villus motility in the absorptive function of the small intestine.
gastrointestinal; intestine; gut; absorption; villi; lattice Boltzmann method
Gastric flow and mixing studied using computer simulation.
Proceedings of the Royal Society B: Biological Sciences
The fed human stomach displays regular peristaltic contraction waves that originate in the proximal antrum and propagate to the pylorus. High-resolution concurrent manometry and magnetic resonance imaging (MRI) studies of the stomach suggest a primary function of antral contraction wave (ACW) activity unrelated to gastric emptying. Detailed evaluation is difficult, however, in vivo. Here we analyse the role of ACW activity on intragastric fluid motions, pressure, and mixing with computer simulation. A two-dimensional computer model of the stomach was developed with the 'lattice-Boltzmann' numerical method from the laws of physics, and stomach geometry modelled from MRI. Time changes in gastric volume were specified to match global physiological rates of nutrient liquid emptying. The simulations predicted two basic fluid motions: retrograde 'jets' through ACWs, and circulatory flow between ACWs, both of which contribute to mixing. A well-defined 'zone of mixing', confined to the antrum, was created by the ACWs, with mixing motions enhanced by multiple and narrower ACWs. The simulations also predicted contraction-induced peristaltic pressure waves in the distal antrum consistent with manometric measurements, but with a much lower pressure amplitude than manometric data, indicating that manometric pressure amplitudes reflect direct contact of the catheter with the gastric wall. We conclude that the ACWs are central to gastric mixing, and may also play an indirect role in gastric emptying through local alterations in common cavity pressure.
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