Mammalian urine concentration: a review of renal medullary architecture and membrane transporters

C. Michele Nawata, Thomas L. Pannabecker

Research output: Contribution to journalReview articlepeer-review

23 Scopus citations


Mammalian kidneys play an essential role in balancing internal water and salt concentrations. When water needs to be conserved, the renal medulla produces concentrated urine. Central to this process of urine concentration is an osmotic gradient that increases from the corticomedullary boundary to the inner medullary tip. How this gradient is generated and maintained has been the subject of study since the 1940s. While it is generally accepted that the outer medulla contributes to the gradient by means of an active process involving countercurrent multiplication, the source of the gradient in the inner medulla is unclear. The last two decades have witnessed advances in our understanding of the urine-concentrating mechanism. Details of medullary architecture and permeability properties of the tubules and vessels suggest that the functional and anatomic relationships of these structures may contribute to the osmotic gradient necessary to concentrate urine. Additionally, we are learning more about the membrane transporters involved and their regulatory mechanisms. The role of medullary architecture and membrane transporters in the mammalian urine-concentrating mechanism are the focus of this review.

Original languageEnglish (US)
Pages (from-to)899-918
Number of pages20
JournalJournal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
Issue number6
StatePublished - Nov 1 2018
Externally publishedYes


  • Aquaporins
  • Kidney
  • Renal medulla
  • Urea transporters

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry
  • Physiology
  • Animal Science and Zoology
  • Endocrinology


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