Going with the flow: updating old techniques to gain insight into regional kidney hemodynamics

摘要

Renal blood flow occurs both in series and parallel. Whileall the blood entering the kidney first enters the renal cortex,two distinct populations of nephrons give rise to remarkablydifferent post-glomerular capillary circulations. Superficialand mid-cortical nephrons give rise to the cortical peritubular capillary network, a web of capillaries that supplies thecortical parenchyma and supports reabsorption of the bulkof the glomerular filtrate. In contrast, the majority of juxtamedullary nephrons, whose afferent arterioles arise near thecorticomedullary junction, give rise to vascular bundles containing descending vasa recta capillaries that supply blood tothe renal medulla. Some of these descending vasa recta traverse all the way to the tip of the papilla, before loopingaround to giving rise to ascending vasa recta capillaries.Descending vasa recta on the periphery of these vascularbundles give rise to the dense plexus of capillaries that supply the medullary parenchyma. The relatively low rate ofperfusion (less than 10% of total renal blood flow) and thelooped structure of the medullary circulation limit the washout of solutes including NaCl and urea in this region, maximizing the ability to form concentrated urine.