Investigating the relationships between peristaltic contraction and fluid transport in the human colon using Smoothed Particle Hydrodynamics

© 2012. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Complex relationships exist between gut contractility and the flow of digesta. We propose here a Smoothed Particle Hydrodynamics model coupling the flow of luminal content and wall flexure to help investigate these relationships. The model indicates that a zone of muscular relaxation preceding the contraction is an important element for transport. Low pressures in this zone generate positive thrust for low viscosity content. The viscosity of luminal content controls the localization of the flow and the magnitude of the radial pressure gradient and together with contraction amplitude they control the transport rate. For high viscosity content, high lumen occlusion is required for effective propulsion

But what do the numbers say? How the movement towards datafication might change English higher education

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A tale of two objectives: The challenge of meeting diverse targets in UK Business School

Business Schools in Great Britain are currently facing a number of major challenge due to the conflicting objectives that need to be met. The movement towards a metric-driven, performative approach that has occurred in the last decade has meant that the need to meet set measures that focus on the outcomes of students’ study have become imperative. However, focusing solely on these outcomes neglects a second set of objectives that relate to the journey students take during their studies. The need to ensure that both the process and the outcome of students’ studies are stressed is particularly challenging in British Business Schools which are often characterised by a large and diverse student and staff population. This think piece posits that by using a loose/tight cultural approach alongside a Schrödinger's leadership style, leaders can mitigate some of the challenges that are currently faced in the sector

Circadian rhythms in colonic function

PUBLISHED 30 August 2023A rhythmic expression of clock genes occurs within the cells of multiple organs and tissues throughout the body, termed “peripheral clocks.” Peripheral clocks are subject to entrainment by a multitude of factors, many of which are directly or indirectly controlled by the light-entrainable clock located in the suprachiasmatic nucleus of the hypothalamus. Peripheral clocks occur in the gastrointestinal tract, notably the epithelia whose functions include regulation of absorption, permeability, and secretion of hormones; and in the myenteric plexus, which is the intrinsic neural network principally responsible for the coordination of muscular activity in the gut. This review focuses on the physiological circadian variation of major colonic functions and their entraining mechanisms, including colonic motility, absorption, hormone secretion, permeability, and pain signalling. Pathophysiological states such as irritable bowel syndrome and ulcerative colitis and their interactions with circadian rhythmicity are also described. Finally, the classic circadian hormone melatonin is discussed, which is expressed in the gut in greater quantities than the pineal gland, and whose exogenous use has been of therapeutic interest in treating colonic pathophysiological states, including those exacerbated by chronic circadian disruption.Timothy J. Hibberd, Stewart Ramsay, Phaedra Spencer-Merris, Phil G. Dinning, Vladimir P. Zagorodnyuk and Nick J. Spence

Neural mechanisms of peristalsis in the isolated rabbit distal colon: a neuromechanical loop hypothesis

Published online: 16 April 2014.Propulsive contractions of circular muscle are largely responsible for the movements of content along the digestive tract. Mechanical and electrophysiological recordings of isolated colonic circular muscle have demonstrated that localized distension activates ascending and descending interneuronal pathways, evoking contraction orally and relaxation anally. These polarized enteric reflex pathways can theoretically be sequentially activated by the mechanical stimulation of the advancing contents. Here, we test the hypothesis that initiation and propagation of peristaltic contractions involves a neuromechanical loop; that is an initial gut distension activates local and oral reflex contraction and anal reflex relaxation, the subsequent movement of content then acts as new mechanical stimulus triggering sequentially reflex contractions/relaxations at each point of the gut resulting in a propulsive peristaltic contraction. In fluid filled isolated rabbit distal colon, we combined spatiotemporal mapping of gut diameter and intraluminal pressure with a new analytical method, allowing us to identify when and where active (neurally-driven) contraction or relaxation occurs. Our data indicate that gut dilation is associated with propagating peristaltic contractions, and that the associated level of dilation is greater than that preceding non-propagating contractions (2.7 ± 1.4 mm vs. 1.6 ± 1.2 mm; P < 0.0001). These propagating contractions lead to the formation of boluses that are propelled by oral active neurally driven contractions. The propelled boluses also activate neurally driven anal relaxations, in a diameter dependent manner. These data support the hypothesis that neural peristalsis is the consequence of the activation of a functional loop involving mechanical dilation which activates polarized enteric circuits. These produce propulsion of the bolus which activates further anally, polarized enteric circuits by distension, thus closing the neuromechanical loop.Phil G. Dinning, Lukasz Wiklendt, Taher Omari, John W. Arkwright, Nick J. Spencer, Simon J. H. Brookes and Marcello Cost

The impact of laxative use upon symptoms in patients with proven slow transit constipation

<p>Abstract</p> <p>Background</p> <p>Constipation severity is often defined by symptoms including feelings of complete evacuation, straining, stool frequency and consistency. These descriptors are mostly obtained in the absence of laxative use. For many constipated patients laxative usage is ubiquitous and long standing. Our aim was to determine the impact of laxative use upon the stereotypic constipation descriptors.</p> <p>Methods</p> <p>Patients with confirmed slow transit constipation completed 3-week stool diaries, detailing stool frequency and form, straining, laxative use and pain and bloating scores. Each diary day was classified as being under laxative affect (laxative affected days) or not (laxative unaffected days). Unconditional logistic regression was used to assess the affects of laxatives on constipation symptoms.</p> <p>Results</p> <p>Ninety four patients with scintigraphically confirmed slow transit constipation were enrolled in the study. These patients reported a stool frequency of 5.6 ± 4.3 bowel motions/week, only 21 patients reported <3 bowel motions/week. Similarly, 21 patients reported a predominant hard stool at defecation. The majority (90%) of patients reported regular straining. A regular feeling of complete evacuation was reported in just 7 patients. Daily pain and/or bloating were reported by 92% of patients. When compared with laxative unaffected days, on the laxative affected days patients had a higher stool frequency (OR 2.23; <it>P </it><0.001) and were more likely to report loose stools (OR 1.64; <it>P </it><0.009). Laxatives did not increase the number of bowel actions associated with a feeling of complete evacuation. Laxative use had no affect upon straining, pain or bloating scores</p> <p>Conclusions</p> <p>The reporting of frequent and loose stools with abdominal pain and/or bloating is common in patients with slow transit constipation. While laxative use is a significant contributor to altering stool frequency and form, laxatives have no apparent affect on pain or bloating or upon a patients feeling of complete evacuation. These factors need to be taken into account when using constipation symptoms to define this population.</p