The association of vasa recta with the loops of Henle and collecting ducts forms the anatomic substrate for the countercurrent exchange system, which is critical for the production of concentrated urine (see Plate 3-12). Some illustrations depict each individual nephron as being consistently associated with the vasa recta derived from its own efferent arteriole. It is now understood, however, that each nephron is invested with vasa recta derived from numerous efferent arterioles.

Advanced age and certain types of chronic kidney disease are associated with degeneration of glomerular vessels. In the cortex, this is often enough to obliterate postglomerular flow altogether. Near the medulla, where the efferent arterioles are thicker, such degeneration gives rise to aglomerular shunts that connect afferent and efferent arterioles. In this case, vasa recta may emerge directly from arcuate and interlobular arteries.