The Loop of Henle (LoH) is a long, straight, tubular segment connecting the proximal tubule to the distal convoluted tubule and lies parallel to the collecting ducts. The LoH descends from the cortex or medulla (depending on the size/length of the nephron) into the papilla of the kidney.
The LoH consists of three major segments: descending thin limb, ascending thin limb, and ascending thick limb. These segments are characterized by cellular morphology and anatomic location, but also correlate with function. Approximately 15–25% of filtered NaCl is reabsorbed through the LoH, primarily via the thick ascending limb. The LoH plays a critical role in urinary concentration by contributing to the generation of a hypertonic medullary interstitium in a process called countercurrent multiplication. In addition, it contributes to reabsorption of calcium and magnesium ions. The LoH is the site of action of loop diuretics, the most potent class of diuretic agents.