Thin limb

water reabsorptiondriving force: osmotic — due to hypertonic medullary fluidno active salt reabsorption, solutes osmotic pressure will inhibit water reabsorption

Thick ascending limb of the loop of Henle:

active sodium chloride reabsorption 35%impermeable to watersince reabsorption of sodium chloride at this site dilutes the fluid in the tubule, this segment may be referred to as “diluting segment.”Reabsorption of sodium chloride in the thick ascending limb is dependent upon the Na/K/2Cl co-transporter.Normal activity of this transporter and Na/K ATPase results in an increase in intracellular potassium, potassium efflux, and a lumen-positive electrical potential:This lumen-positive membrane potential provides the driving force for reabsorption of magnesium and calcium cations.Therefore loop diuretics which inhibit the action of the sodium potassium chloride co-transporter, leading to increase sodium excretion also leads to increased magnesium and calcium loss.