This document summarizes mechanisms for regulating water and sodium levels in the body. Water regulation occurs through urine concentration and dilution. Diluted urine formation is a simple process using ADH inhibition. Concentrated urine formation is more complex, relying on a hyperosmotic renal medulla maintained by countercurrent exchange in the loop of Henle and vasa recta, and urea recirculation. High ADH levels also aid concentrated urine by pulling water from collecting ducts into the hyperosmotic medulla. These mechanisms allow the kidneys to excrete water and solutes while maintaining osmolarity within a viable range.

1. Control of extracellular osmolarity Water & Na regulation : Dr. M.A.M.Shaikhani.