2014/06/26 by Patricia Yang, Jonathan Pham, Jerome Choo +1 · 1 voice · 2 citations
Engineering · Medicine · #Fluid Dynamics and Turbulent Flows #Urinary Bladder and Prostate Research #Urological Disorders and Treatments
paper · pdf · doi:10.1073/pnas.1402289111
openalex publication_date 2014/06/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Many urological studies rely on models of animals, such as rats and pigs, but their relation to the human urinary system is poorly understood. Here, we elucidate the hydrodynamics of urination across five orders of magnitude in body mass. Using high-speed videography and flow-rate measurement obtained at Zoo Atlanta, we discover that all mammals above 3 kg in weight empty their bladders over nearly constant duration of 21 ± 13 s. This feat is possible, because larger animals have longer urethras and thus, higher gravitational force and higher flow speed. Smaller mammals are challenged during urination by high viscous and capillary forces that limit their urine to single drops. Our findings reveal that the urethra is a flow-enhancing device, enabling the urinary system to be scaled up by a factor of 3,600 in volume without compromising its function. This study may help to diagnose urinary problems in animals as well as inspire the design of scalable hydrodynamic systems based on those in nature.