One of the major functions of the kidneys in maintaining normal fluid balance is:

Major functions of the kidneys in maintaining normal fluid balance include regulation of extracellular fluid and osmolarity by selective retention and excretion of fluids, regulation of pH of the extracellular fluid by retention of hydrogen ions, and excretion of metabolic wastes and toxic substances. ADH is manufactured by the pituitary, and the parathyroid regulates calcium and phosphate balance.Physiological Adaptation