Because of these factors, the concentration of the urine increases dramatically in the descending limb.

[3] The epithelium in the thick segment of the descending limb consists of low simple cuboidal cells, which resemble those found in the proximal tubule.

In contrast, the epithelium transitions to a simple squamous type in the thin segment, which is less metabolically active and has minimal surface specializations.

However, this distinction is not as important physiologically as in the ascending limb, so often the two are treated as one structure.

This article incorporates text in the public domain from page 1223 of the 20th edition of Gray's Anatomy (1918)