Renal medullary circulation.

The renal medullary microcirculation is a distinctive arrangement of blood vessels that serve multiple functions in the renal medulla. This article begins with a description of the unique anatomy of this vascular bed and the role it plays in transport and countercurrent exchange in the medulla. A segment of the review is then devoted to the important role mathematical modeling has played in the understanding of this vascular bed's function. Succeeding sections focus upon the hematocrit in the vasa recta capillaries and methods utilized to assess blood flow in the renal medulla. An extensive portion of the article is then devoted to the regulation of the medullary circulation, from ion channel architecture to neurohormonal signaling. Finally, we discuss the importance of the renal medullary circulation in the regulation of fluid and electrolyte homeostasis and arterial blood pressure regulation.