In the distal convoluted tubule, final adjustments are made to the composition of urine. It is here that the hormone aldosterone influences the resorption of sodium, in order to keep the levels of salt in the extracellular fluid and the blood stream constant.
For example, on a hot day the body may loose salt in the form of sweat. Low levels of salt in the plasma raises levels of aldosterone. This hormone acts on the tubule cells to increase the resorption of sodium from the ultrafiltrate back into the blood stream.
If salt levels are elevated, which could be caused by eating high levels in the diet, the levels of aldosterone in the blood are unaffected. This allows excess salt to be excreted from the nephron in the urine.