Medullary interstitium

The medullary interstitium is the tissue surrounding the loop of Henle in the renal medulla.

It functions in renal water reabsorption by building up a high hypertonicity, which draws water out of the thin descending limb of the loop of Henle and the collecting duct system. This hypertonicity, in turn, is created by a an efflux of urea from the inner medullary collecting duct. .