Flow and mixing by small intestine villi

Area of Science:

• Physiology
• Biophysics
• Computational Fluid Dynamics

Background:

• Small intestine nutrient absorption and mixing are complex multi-scale processes.
• Flow dynamics at the villi scale (≈500 μm) remain poorly understood.
• Understanding these micro-scale flows is crucial for comprehending nutrient absorption.

Purpose of the Study:

• To investigate the hydrodynamic effects of villous movements on flow, mixing, and nutrient absorption.
• To model the influence of digesta rheology on these processes at the intestinal periphery.
• To elucidate the role of villous contractions in radial mass transfer.

Main Methods:

• Developed a three-dimensional lattice-Boltzmann model.
• Simulated hydrodynamic consequences of villi movements due to mucosal folding during longitudinal contractions.
• Analyzed the impact of nutrient diffusivity and fluid shear-thinning (pseudoplasticity) on mass transfer.

Main Results:

• Cyclic villi approximation and separation generated laminar eddies, enhancing radial mass transfer.
• Augmented mass transfer improved nutrient absorption and mixing at the intestinal periphery.
• Increased nutrient diffusivity and fluid pseudoplasticity further enhanced these effects.

Conclusions:

• Villous movements during longitudinal contractions are a significant radial mixing mechanism in the small intestine.
• These movements enhance mixing and absorption near the mucosa, overcoming adverse rheological conditions.
• The findings provide critical insights into the micro-scale fluid dynamics governing intestinal function.