SUMMARYBranches of tortuous arteries in the adventitia of the minor calyces supply blood to the renal papilla. The papilla therefore receives blood from both the vasa recta and the calyx.In certain pathological conditions this dual blood supply is of importance. It probably accounts for the preservation of the papilla and adjacent medulla in cases of acute tubular necrosis. When the calycine vessels are occluded, any interference with the blood supply through the vasa recta, such as occurs during peripheral circulatory failure, is liable to lead to ischemic necrosis of the renal papilla.