Chapter 35 - Water and Electrolytes Homeostasis

Abstract

This chapter describes factors regulating intake and loss of water and electrolytes. At the cellular level, the Na+/K+-ATPase plays a principal role in maintaining cellular hydration and ion content. It also exerts a major effect on other cellular ion transport systems. Water flows between major body fluid compartments (intracellelar fluid (ICF) and extracellular fluid (ECF) are regulated by the osmotic pressure. The movement of fluid between the plasma and ECF depends on the balance between the hydrostatic and oncotic pressures.Water and electrolyte balance is subject to neurohormonal regulation through the renin–angiotensin–aldosterone system and the actions of vasopressin. The kidney is the main organ which maintains water and electrolyte balance. Blood and urine testing, and particularly the tests of renal function are essential in the assessment of the water and electrolite disorders. Dehydration or overhydration, often together with abnormal plasma sodium and potassium concentrations, are commonly seen in medical practice. The hyper- and hyponatremia and hyper- and hypokalemia are the most common electrolyte abnormalities. Physician’s approach to a patient with a suspected fluid and electrolyte disorder includes physical examination, history, biochemical testing and the assessment of daily water and electrolyte intake and loss.