Aldosterone is the major hormone responsible for maintaining sodium balance in the extracellular fluid. Antidiuretic hormone, also called ADH or vasopressin, helps control water balance.
Aldosterone is released by the adrenal cortex in response to a protein called angiotensin, produced by the kidneys. Once the adrenal glands release aldosterone, it returns to the kidneys and promotes sodium retention.
In conjunction with its receptor, aldosterone turns on a gene encoding a sodium channel. After a number of these sodium channels are produced, they are inserted into the membranes of cells in the kidneys' collecting ducts, where they increase sodium reuptake.
People with aldosterone deficiency develop low sodium and abnormally low blood pressure.
ADH works in a similar way to prevent water loss in urine. This hormone is released by the posterior pituitary when brain sensors detect that extracellular fluid is becoming too thick or syrupy. ADH travels to the kidneys, where it triggers the insertion of special water channels called aquaporins into the cell membranes.
People who make insufficient ADH (or whose kidneys do not respond to ADH) develop a condition called diabetes insipidus, marked by excessive urination.