Kidneys are a major excretory organ that maintains the body's internal enviornment by regulating total water volume and total solute concentration in water, regulataing ion concentrations in extracellular fluid, ensuring long-term acid-base balance, excreting metabloic wastes, toxins, drugs, producing erythropoeitin which regiulates blood pressure and renin, activates vitamin D and carries out gluconeogenesis if needed.