Vasa recta (kidney)

A nephron, the vasa recta is labelled arteria recta

The vasa recta is a loop of the renal circulation that surrounds the Loop of Henle, part of the nephron in the medulla of the kidney. This loop of capillaries branches off the arcuate arterioles, from the pelvis and descends into the medulla. It returns blood to the arcuate venules, with varied solute concentrations, depending on the concentration of urine being produced. This arrangement is essential in the mechanism of the countercurrent multiplier, which concentrates the urine.