Schematic diagram of a cross section through the outer stripe, inner stripe, upper inner medulla (IM), mid IM, and deep IM, showing regions and relative positions of tubules and vessels. Decimal numbers indicate relative interaction weightings with regions. R1, R2, R3, and R4, regions in the outer medulla; R5, R6, and R7, regions in the IM. SDL, descending limbs of short loops of Henle. SAL, ascending limbs of long loops of Henle. LDL, descending limb of long loop of Henle. LAL, ascending limb of long loop of Henle. Subscripts “S,” “M,” and “L” associated with an LDL or LAL denote limbs that turn with the first mm of the IM (S), within the mid IM (M), or reach into the deep IM (L). CD, collecting duct. SDV, short descending vasa recta. SAV3 and SAV4, two populations of short ascending vasa recta. LDV, long descending vas rectum. LAV1, LAV2, …, LAV7, populations of long ascending vasa recta. Reprinted from [45].