In the blood supply of the kidney, the vasa recta form a series of straight capillaries (recta is from the Latin for "straight") that descend from the cortex into the medulla. These vessels branch off of the efferent arterioles of juxtamedullary nephrons (those nephrons closest to the medulla), enter the medulla, and surround the loop of Henle.

Each of the vasa recta has a hairpin turn in the medulla and carries blood at a very slow rate, two factors crucial in the maintenance of countercurrent exchange that prevent washout of the concentration gradients established in the renal medulla. The maintenance of this concentration gradient is one of the components responsible for the kidney's ability to produce concentrated urine.

The slow blood flow in vasa recta makes them a likely place of thrombosis in hypercoagulable states, or erythrocyte sickling in sickle cell disease. Ischemia that results may lead to renal papillary necrosis.

Kidney