The Obstructed Kidney

SUMMARY Ureteric obstruction raises the pressure in the collecting system to a point at which glomerular filtration ceases. Diodrast can still be cleared from the blood in the peri‐tubular capillaries by the tubule cells. The raised tubular pressure is transmitted to the peritubular capillaries, and so to the efferent arterioles, distending the glomerular enden‐chyme. The small arterial vessels of the renal cortex have thus become engorged, and diffusion from the peri‐tubular vessels will increase the interstitial fluid. The substance of the kidney has thus increased, raising the pressure within the renal capsule with the combined effect of producing pain and reducing renal artery blood flow. The local circulation described by Hinman will allow concentrated contrast to pass from the collecting tubules into the minor calyces adjacent to the papillae. When the obstruction ceases, the supernormal pressures within the renal capsule can return to normal by an immediate emptying of all surplus dye‐laden fluid–vascular, interstitial, cellular and intra luminal–into the ureter. This restores the renal size to normal and wipes out the nephrogram as the molecules of dye are flushed out into the collecting system and into the renal pelvis.