The physiology of urinary concentration: an update.

Journal Article (Review;Journal Article)

The renal medulla produces concentrated urine through the generation of an osmotic gradient extending from the cortico-medullary boundary to the inner medullary tip. This gradient is generated in the outer medulla by the countercurrent multiplication of a comparatively small transepithelial difference in osmotic pressure. This small difference, called a single effect, arises from active NaCl reabsorption from thick ascending limbs, which dilutes ascending limb flow relative to flow in vessels and other tubules. In the inner medulla, the gradient may also be generated by the countercurrent multiplication of a single effect, but the single effect has not been definitively identified. There have been important recent advances in our understanding of key components of the urine concentrating mechanism. In particular, the identification and localization of key transport proteins for water, urea, and sodium, the elucidation of the role and regulation of osmoprotective osmolytes, better resolution of the anatomical relationships in the medulla, and improvements in mathematic modeling of the urine concentrating mechanism. Continued experimental investigation of transepithelial transport and its regulation, both in normal animals and in knock-out mice, and incorporation of the resulting information into mathematic simulations, may help to more fully elucidate the inner medullary urine concentrating mechanism.

Full Text

Duke Authors

Cited Authors

  • Sands, JM; Layton, HE

Published Date

  • May 2009

Published In

Volume / Issue

  • 29 / 3

Start / End Page

  • 178 - 195

PubMed ID

  • 19523568

Pubmed Central ID

  • PMC2709207

Electronic International Standard Serial Number (EISSN)

  • 1558-4488

International Standard Serial Number (ISSN)

  • 0270-9295

Digital Object Identifier (DOI)

  • 10.1016/j.semnephrol.2009.03.008


  • eng