Peristalsis in Action: A Bio-fluid Dynamics Perspective of Bile Transport and Gastrointestinal Motility

Abstract

Bile salts play a crucial role in lipid digestion by emulsifying fats into micelles, enhancing enzymatic hydrolysis by lipases. This process is not solely chemically driven but is significantly influenced by small intestinal peristalsis. Small intestinal peristalsis provides a significant advantage by slowing the reaction kinetics and accelerating the duodenum's micelle formation. Biliary reflux, the backflow of bile and other alkaline duodenal contents into the stomach leads to gastric inflammation, metaplasia, and carcinogenesis. This reflux, known as duodenogastric reflux (DGR), is linked to gastroduodenal motility, which refers to the coordinated contractions of the stomach (antrum), pylorus, and duodenum that regulate the movement of food and digestive fluids. However, the precise mechanisms that govern how and why bile refluxes into the stomach remain unclear. This study presents a mathematical model to investigate bile transport as a non-reactive species within the antropyloroduodenal segment, considering its non-Newtonian nature as a power-law fluid. Utilizing the lubrication approximation, exact analytical solutions are derived and validated through MATLAB simulations. Bile transport is analyzed under various duodenal motility patterns such as elementary contraction like antegrade propagating waves (APW), retrograde propagating waves (RPW), and stationary waves (SW), with variations in wavelength, wave velocity, occlusion, and contraction frequency. Results indicate that bile transport is driven mainly by wave traversal in the duodenum, with increased occlusion leading to more extended particle displacement [90% occlusion resulting in greater transit than 70% occlusion]. In contrast, pyloric resistance, influenced by channel width, impedes transport, contributing to oscillatory excursions. The findings underscore the coordinated influence of antral, pyloric, and duodenal motility in regulating bile flow and its impact on gastric physiology.