At the inner medulla near the renal papilla, the collecting tubules converge to form papillary ducts, which convey urine into the pelvicalyceal space. The papillary ducts are lined by a layer of columnar or high columnar epithelial cells; they have a structure similar to that lining the collecting tubules. In addition to the papillary ducts, only thin segments of Henles loop approach this inner zone. They run down to this zone and return to the outer medulla. There are no histological differences between the descending and ascending thin segment of Henles loop.