Changes

Due to the transport of sodium and chloride from the thick ascending limb, as the fluid passes up this limb the concentration of the urine decreases back down to around the level it was when it entered the loop.  However the volume is greatly reduced.  The [[Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology#Collecting Duct| collecting duct]] is where most concentration happens however it is only possible thanks to the incredibly high concentrations of NaCl at the bottom of the loop.  This returning of the concentration back to the same level as when it entered the loop is important for retaining salt and also allows the concentration to be finely controlled by the collecting ducts without the loss of salt.

Due to the transport of sodium and chloride from the thick ascending limb, the concentration of the urine as it passes up this limb decreases back down to around the level it was when it entered the loop.  However the volume is greatly reduced.  The [[Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology#Collecting Duct| collecting duct]] is where most concentration happens however it is only possible thanks to the incredibly high concentrations of NaCl at the bottom of the loop.  This returning of the concentration back to the same level as when it entered the loop is important for retaining salt and also allows the concentration to be finely controlled by the collecting ducts without the loss of salt.