The renal structure, the characteristics of the cortex and the medulla in relation to irrigation and interstitial osmolarity are briefly described. The tubular permeability to water is described throughout the nephron. The function of antidiuretic hormone (ADH) or vasopressin develops. The dilutive segment with its Na, K, 2Cl cotransporters (NKCC) is described. Collecting ducts and how ADH regulates the expression of aquaporins 2 in the apical membrane is described. In this context, the vital importance of extracellular osmolarity as a determinant of thirst and ADH concentration is highlighted. Finally, it is shown how concentrated or diluted urine is produced depending on the extracellular osmolarity detected by the sed-ADH system (osmoregulatory center). I share the link of my channel.    / @mauriciogiuliodori