The Influence Of Pendular Activity On Mass Transfer And Absorption In Rat Duodenum With Villi Taken Into Account

Given the complex motility of the intestinal wall featuring villous structure,the mechanisms by which the motility can enhance mass transfer and absorption in the small intestine have been a mystery for many years.In this work,a multiphysics model has been developed to simulate fluid flow and mass transfer in the lumen driven by the movement of intestinal wall.A unique feature of the model is to implement movement of hierarchical structured wall using a moving mesh method.In this way,the effects of motility of an entire duodenum featuring villi on the mass transfer and absorption under the influence of the surrounding flow field can be systematically explored.It is revealed that the top of the villi plays a major role in mass absorption.For the rat duodenum,the pendular movement can enhance mass transfer and absorption by up to about 72%.With the introduction of ambient bulk flow,although the absorption amount increases,the enhancement of mass transfer by pendular activity is inhibited.Specifically,the average enhancement factor decreases sharply from about 1.35 to about 1.05.Comparison between systems with and without villi were further carried out.It has been found that:(1)with pendular activity,when there is no ambient flow,the mass absorption is underestimated by using smooth intestinal wall instead of villous intestinal wall.With the increase of villous length,the underestimation increases from 30%to about 50%.When the ambient flow is introduced,the mass absorption is overestimated when the length of the villus is 0.35 mm;the mass absorption is underestimated when the length of the villus is greater than 0.35 mm,and the underestimation increases with the length of the villus.(2)For the cases without pendular activity,when there is no ambient flow,the mass absorption is underestimated.As the length of the villus increases,the underestimation increases from 30%to about 50%.When the ambient flow is introduced,the mass absorption is overestimated when the length of the villus is 0.35 mm and 0.4 mm;the mass absorption is underestimated when the length of the villus is greater than 0.4 mm,and the underestimation increases with the increase of the length of the villus.