Three‐dimensional architecture of nephrons and vessels in the human renal medulla

Three‐dimensional architecture of nephrons and blood vessels of the rodent medulla has been shown to have significant impact on mathematical models of the urine concentrating mechanism. We aim to assess potential roles of spatial arrangements of loop of Henle and vessel subsegments that may underlie multiple countercurrent systems in the human renal inner (IM) and outer (OM) medulla. Architecture of medullary nephrons and vessels was assessed with digital reconstructions from physical tissue sections. Tubules and vessels were identified by indirect immunofluorescence using antibodies and lectins that recognize segment‐specific proteins. AQP1‐positive descending thin limbs (DTLs) and UT‐B‐positive descending vasa recta (DVR) are expressed throughout the IM from tip to base. The pelvic wall also expresses UTB. The density of these DTLs and DVR declines with increasing depth below the OM‐IM boundary. DVR are collected into vascular bundles in the OM and initial IM; these vessels become dispersed with increasing depth below the OM‐IM boundary. DTLs and DVR are arranged around the periphery of clusters of AQP2‐positive collecting ducts in the outer zone of the IM, and thus exhibit non‐uniform distribution. This contrasts with the uniform distribution of ClC‐K‐positive ascending thin limbs and prebend segments. This architecture qualitatively resembles that of the rodent medulla. NIH DK16294