SUMMARY

Animals maintain metabolism with food processing and excretion. The organs in digestive and urinary systems have evolved to transport fluids in different forms such as urine, chyme, feces, and fart. We propose to elucidate the anatomical and kinematic adaptations of the systems based on the properties of fluids in the gastrointestinal tract. In our preliminary work, we found that the urethra serves as a siphon to accelerate urine flow by gravity, enabling the urinary system to be scaled up without compromising its function. In this thesis proposal, we will investigate the defecation process and the digestive system. We hypothesize that mucus layer in the large intestine lubricates the wall of intestine across animal sizes. We will perform a combination of comparative anatomy measurements, fluid rheology measurements, high-speed and thermal videography, in vitro surgery, and non-invasive gastrointestinal tract mobility monitoring. We aim to reveal the kinematics of small intestine, cecum and gas transportation with simple scaling analysis. These studies will shed light on the optimal transport strategies in soft tissue, and will provide guiding principles for the design of scalable hydrodynamic systems.