Anaes · Applied cardiovascular & respiratory physiology
Renal: RAAS & water/electrolyte handling
Also known as Renin-angiotensin-aldosterone system · RAAS · Aldosterone · Water balance · ADH · Countercurrent system
The kidney defends blood pressure, sodium, water and potassium through the renin-angiotensin-aldosterone system and a set of linked endocrine loops. The framework rests on five exam-critical ideas: the RAAS is activated by a fall in renal perfusion or sodium or by sympathetic tone, and it restores them through renin, angiotensin II (vasoconstriction, aldosterone release, ADH and thirst) and aldosterone (distal sodium reabsorption and potassium and hydrogen excretion); aldosterone acts on the principal cells of the distal nephron to reabsorb sodium (ENaC) and excrete potassium and hydrogen, linking sodium volume to potassium and acid-base; water balance is governed by ADH (and thirst) via osmoreceptors, ADH inserting aquaporin-2 channels in the collecting duct; the countercurrent multiplier (the loop of Henle) builds the medullary gradient that lets ADH concentrate the urine; and natriuretic peptides (ANP, BNP) from the atria and ventricles oppose the RAAS by promoting sodium excretion. Built on the renal-transporter dimorphism study (Xiong 2026), the hypernatraemia pathophysiology review (Drummond 2026), the sodium and water disorders review (Gilbert 2025), the water-homeostasis review (D'Acierno 2025), the SGLT2 cardiovascular-protection review (Wang 2026), and the chloride-RAAS study (Adin 2026).
Practise this topic
On this page & tools
Your progress
Saved locally on this device.
8 MCQs with explanations
Target exams
Red flags
Meet the patient
A 69-year-old with heart failure takes ramipril, spironolactone and furosemide. She is fasted for surgery. Her preoperative potassium is 5.7 mmol per L, and at induction her systolic pressure collapses to 80 mmHg. The same system that was protecting her heart is now the one failing her blood pressure and her potassium.[2][3]
The question this topic answers is: how does the kidney defend volume and pressure, and what happens when we block that defence perioperatively? Two hormones do most of the work — angiotensin II holds the pressure, aldosterone holds the sodium — and a third, ADH, holds the water. Her three drugs have dismantled each in turn.[1]
You have read the opening of this topic. The complete unit — every section and its primary-source references — is part of the Anaesthesia fellowship atlas.
References6Show ledgerHide ledger
- [1]Xiong LI, et al. Sexual dimorphic pattern of renal transporters and channels in spontaneously hypertensive rats Am J Physiol Cell Physiol, 2026.PMID 42290570
- [2]Drummond JB. Pathophysiology and aetiologies of hypernatremia Best Pract Res Clin Endocrinol Metab, 2026.PMID 41176477
- [3]Gilbert SJ. Sodium and Water Disorders Adv Kidney Dis Health, 2025.PMID 40175029
- [4]D'Acierno M, et al. The biology of water homeostasis Nephrol Dial Transplant, 2025.PMID 39435642
- [5]Wang Z, et al. Cardiovascular protection by SGLT2 inhibitors: an integrative review of mechanistic networks, clinical evidence, and safety considerations Front Cardiovasc Med, 2026.PMID 42344351
- [6]Adin D, et al. Influence of serum chloride concentrations on the renin-angiotensin-aldosterone system in dogs with congestive heart failure Am J Physiol Renal Physiol, 2026.PMID 42324236