title: Three-dimensional simulation of urine concentrating mechanism in a functional unit of rat outer medulla. I. Model structure and base case results.
abstract: The urine formation and excretion system have long been of interest for mathematicians and physiologists to elucidate the obscurities within the process happens in renal tissue. In this study, a novel three-dimensional approach is utilized for modeling the urine concentrating mechanism in rat renal outer medulla which is essentially focused on demonstrating the significance of tubule's architecture revealed in anatomic studies and physiological literature. Since nephrons and vasculatures work interdependently through a highly structured arrangement in outer medulla which is dominated by vascular bundles, a detailed functional unit is proposed based on this specific configuration. Furthermore, due to relatively lesser influence of vasa recta on interstitial medullary osmolality and osmotic gradients as well as model structure simplicity, central core assumption is employed. The model equations are based on three spatial dimensional mass, momentum and species transport equations as well as standard expressions for solutes and water transmural transport. Our model can simulate preferential interactions between different tubules and it is shown that such interactions promote solute cycling and subsequently, enhance urine-concentrating capability. The numerical results are well consistent with tissue slice experiments and moreover, our model predicts more corticomedullary osmolality gradient in outer medulla than previous influential 1-D simulations.
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: Salman
authors.initials: S
authors.lastname: Sohrabi
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran. Electronic address: mssaidi@sharif.edu.
authors.forename: Mohammad Said
authors.initials: MS
authors.lastname: Saidi
authors.affiliation: Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Saadatmand
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: Mohamad Hossein
authors.initials: MH
authors.lastname: Banazadeh
authors.affiliation: Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran.
authors.forename: Bahar
authors.initials: B
authors.lastname: Firoozabadi
mesh_terms: D000818:Animals; D007671:Kidney Concentrating Ability / Q000502:physiology*; D007679:Kidney Medulla / Q000502:physiology*; D008954:Models, Biological; D051381:Rats
keywords: Renal outer medulla; Three-dimensional modeling; Tubule's architecture; Urine concentrating mechanism