Species transport in rat kidney inner medulla

The cumulative pattern in the CDs permeability to urea allows CDs to absorb urea along the IM axis, with the exception of the region very close to the tip of the papilla. Narrow bends cannot make the interstitium concentrated enough. Therefore, in the case of ignoring wide bends, urea concentration declines at the tip of the papilla. On the other hand, by including wide bends, that composes 50% of bend in the papillary, the effect of Henle loops per micrometer of the IM axis increases. Subsequently, high Na+ gradient along the IM axis is produced, and make the region above the papilla more concentrated with Na+. Consequently, more water diffuses out of CDs. Further large surface area between the pre-bend segments and CDs intensifies the gradient between the CDs and Henle loops' walls, and let more water flow out of the CDs.

In this study our focus was on introducing our three-dimensional method in IM modeling by including detailed topographical information about the tubules and using a sophisticated morphology for IM. Results such as concentration contours in the interstitium showed that species distribution in the IM is significantly dependent on the tubules position at each depth that implies the importance of including the topographical information in the modeling. Moreover, in order to assess the direct influence of wide bends, completely three-dimensional modeling is required. Comparison of cases with and without wide bends, exhibited the effect of this feature in the IM to be noticeable with respect to its presence in a small fraction of IM, which once more confirm the necessity of completely three-dimensional modeling.