Fig. 1.

Schematic diagram of a cross section through the upper inner medulla (IM; A), mid-IM (B), and deep IM (C), showing concentric regions and relative positions of tubules and vessels. Decimal numbers in A indicate relative interaction weightings with regions. R1, R2, concentric regions; DTL_S, ATL_S, descending/ascending limb of long loop of Henle that turns within the first millimeter of the IM; DTL_M, ATL_M, descending/ascending limb of long loop of Henle that turns within the mid-IM; DTL_L, ATL_L, descending/ascending limb of long loop of Henle that reaches into the deep IM; CD, collecting duct; DVR, descending vas rectum; AVR₁ and AVR₂ , two populations of ascending vasa recta.