Despite active research, the mechanism by which urine is transported from the kidneys into the urinary bladder remains unclear. In general, the ureteral flow is not purely peristaltic and includes a component which depends on the pressure difference between the renal pelves and the urinary bladder. Thus reflux might be caused by an increase in the pressure inside the bladder. Reflux may result in the ingress of bacteria and toxins from the bladder into the renal pelves and then into the kidneys [1]. In the absence of peristalsis, the ureter behaves as a non-uniform passively distensible tube and the flow through it may be taken as approximately steady. The problem of correctly modeling the smooth muscle of the ureter (like that of many other organs: esophagus, bowels, seminal duct, etc.) is to a large extent unsolved [2,3]. The rate of contraction of the muscle depends on the load against which it is contracting as well as on its current geometry and its state of activation, and that load consists largely of the hydrodynamic (viscous) forces required to move the urine.

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