Osmoregulation versus volume regulation: thirst, ADH release and effective circulating volume
Why plasma sodium reflects water balance and extracellular volume reflects sodium balance, how osmoreceptors and baroreceptors control ADH and thirst, what effective circulating volume means in heart failure and cirrhosis, and how to work through osmolality and saline-in-SIAD calculations.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Two separate control systems:
- Osmoregulation controls water to keep plasma osmolality at 275 to 295 mOsm/kg. Sensor: hypothalamic osmoreceptors. Effectors: ADH and thirst.
- Volume regulation controls sodium to keep effective circulating volume adequate. Sensors: baroreceptors and the juxtaglomerular apparatus. Effectors: RAAS, renal sympathetic nerves, natriuretic peptides, pressure natriuresis, plus ADH when volume falls far.
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Sources
- Brenner and Rector's The Kidney, 11th editionElsevier, 2020
- Therapeutic Guidelines: RenalAU/NZTherapeutic Guidelines Limited, 2026
- Spasovski G, Vanholder R, Allolio B et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol 2014;170:G1-47European Journal of Endocrinology, 2014
- Verbalis JG, Goldsmith SR, Greenberg A et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med 2013;126(10 Suppl 1):S1-42American Journal of Medicine, 2013
- Last updated
- 14 November 2026
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