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Physiology of Sodium

On this page:Sodium Homeostasis


  • Sodium is the principle cation in extracellular fluid. Its extracellular concentration is normally 12 mmol/L, while its extracellular concentration is approximately 140 mmol/L.
    • Roles of Sodium

    • Maintenance of blood volume
    • Maintenance of cellular osmotic pressure gradients
    • Maintance of membrane potentials, and activation of action potentials
    • Nerve conduction
    • Intake

    • Dietary sodium comes from many different sources. Average dietary salt intake is much higher than recommended levels for most western people.
    • Excretion

    • Sodium is primarily excreted by the kidneys; it is freely filtered through the glomerulus and reabsorbed within the proximal convoluted tubule. Sodium is also excreted through sweat, tears, and faeces.

Sodium Homeostasis

  • Pressure natriuresis - increased blood volume and/or pressure will stimulate increased sodium excretion through increased glomerular filtration.
  • Renin-angiotensin-aldosterone system (RAAS) - reduced perfusion within the juxtaglomerular apparatus stimulates renin release, which in turn stimulates the production of angiotensin I. Angiotensin I is converted to angiotensin II by ACE. Angiotensin II modulates pressure natriuresis and increases tubular sodium resorption, both directly and indirectly by stimulating aldosterone.
  • Aldosterone - once secreted by the adrenal cortex will stimulate increased active reabsorption of sodium.
  • Antidiuretic hormone (ADH) - the pituitary gland secretes ADH in response to reduced serum water concentration, which then acts on the distal convoluted tubule to salvage water and concentrate urine.
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