vasa recta
A group of microvessels that are part of the kidney. A vasa recta has a hairpin-like shape, entering the renal medulla as the straight arterioles and surrounds the loop of Henle, forming a capillary network. Finally it leaves the renal medulla to ascend to the cortex as the straight venules. The primary function of the vasa recta is to facilitate countercurrent exchange, which is essential for the kidney's ability to concentrate urine