Regulation of Water and Electrolytes



The internal fluid conditions of the body must be regulated and kept relatively constant for normal body function. Water levels and concentrations of dissolved substances are largely regulated by the urinary system. The kidneys, organs of the urinary system, contain tiny structures called nephrons that filter the blood and produce urine. Useful substances are reabsorbed from the filtrate back into the blood, and other substances are secreted, or removed from the blood. The final product of the nephrons is released as urine. For example, an imbalance in electrolytes, chemicals that dissociate into positive and negative ions in water, can affect the production of urine. The rate of blood filtration, urine volume, and urine concentration can vary to keep electrolytes, water, and pH levels at homeostasis.

At A Glance

  • Fluids inside cells and outside cells differ in composition and water, and solute levels in these fluid compartments must be regulated for normal body functioning.
  • The nephron, the part of the kidney that produces urine, is subdivided into the glomerulus, where blood filtration occurs, and associated tubules, where the blood filtrate is modified.
  • The nephrons are responsible for the filtration of blood and the modification of the filtrate by reabsorption and secretion in order to produce urine.
  • Imbalance in water and electrolytes in the body can result in a change in volume or concentration of urine to keep the body at homeostasis.
  • Osmotic pressure, or the concentration of body fluids, is maintained by water moving freely between intracellular and extracellular compartments under the direction of hormonal input from the kidneys.
  • Blood pH is largely regulated by the kidneys by modifying reabsorption and secretion rates of hydrogen ions and bicarbonate ions to maintain pH balance.