Architecture of nephrons and vessels passing through the transition zone between the outer and inner renal medulla

Nephrons and vessels of the rat inner stripe exhibit architectural arrangements distinct from those of the inner medullary outer zone. Variable‐length morphologically‐distinct subsegments (types 2 and 3) of descending thin limbs of Henle (DTLs) roughly correspond to expression or absence, respectively, of AQP1 and fluid transport along this segment. DTLs enter the IM from various zones of the OM, leading towards variable, but defined, target zones in the IM. Ascending loop segments enter the OM from various zones of the IM, leading towards variable target zones in the OM. For example, short‐long loops of Henle, those that express no detectable inner medullary AQP1, form their bend within the first millimeter below the OM‐IM boundary and ascend through the interbundle zone of the inner stripe, adjacent to their near‐bend CD. Most ascending vasa recta (AVR) pass from IM to OM via vascular bundles. As we showed previously, a population of AVR ascends directly from the intracluster region of the IM into the interbundle region of the OM. These AVR join outer medullary interbundle vascular networks in the deep inner stripe, a fraction of which then join the vascular bundles. Such architecture could play a role in producing fluid and solute axial flows that are involved with producing and sustaining compartments of variable solute concentrations in the many axial and lateral structural zones of the OM and IM. DK16294