Changes

===The Concentrating Mechanism, Aquaporins and ADH===

===The Concentrating Mechanism, Aquaporins and ADH===

Water is drawn from the lumen of the tubule by the increasing hypertonicity of the surrounding tissue as the duct makes its way deeper into the medulla.  However this reabsorption is only possible thanks to [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology|ADH]] inserting [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#What are Aquaporins|aquaporins]] into the apical membrane.  These channels are always present on the basolateral membrane of the epithelial cells but not on the apical membrane.  The reabsorption would not be possible if the urine did not go back up the [[Loop Of Henle - Anatomy & Physiology #Thick ascending limb| thick ascending limb]] of the loop of henle, where its concentration was decreased by the reabsorption of salt, but instead went straight into the collecting ducts.  Although this would mean very concentrated urine it would result in massive salt losses.  Thus the collecting duct allows for very concentrated urine with minimal salt loss. It also allows the concentration of the urine to vary from dilute to concentrated under the control of the hypothalamus and ADH concentrations.

Water is drawn from the lumen of the tubule by the increasing hypertonicity of the surrounding tissue as the duct makes its way deeper into the medulla.  However this reabsorption is only possible thanks to [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology|ADH]] inserting [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#What are Aquaporins|aquaporins]] into the apical membrane.  These channels are always present on the basolateral membrane of the epithelial cells but not on the apical membrane.  The reabsorption would not be possible if the urine did not go back up the [[Reabsorption and Secretion Along the Loop of Henle - Anatomy & Physiology#Thick ascending limb| thick ascending limb]] of the loop of henle, where its concentration was decreased by the reabsorption of salt, but instead went straight into the collecting ducts.  Although this would mean very concentrated urine it would result in massive salt losses.  Thus the collecting duct allows for very concentrated urine with minimal salt loss. It also allows the concentration of the urine to vary from dilute to concentrated under the control of the hypothalamus and ADH concentrations.

==Ions and Compounds==

==Ions and Compounds==