NephrologyTier 2Topic

Acid–base regulation and its link to the respiratory system

Renal and respiratory roles

The kidney maintains acid-base balance by reabsorbing filtered bicarbonate (proximal tubule) and generating new bicarbonate while excreting hydrogen ions (distal tubule, via ammoniagenesis and titratable acid)
Complements the lungs' rapid, short-term compensation (CO2 excretion) - the kidney provides slower, more complete correction over days
Renal compensation for a respiratory acid-base disturbance takes 1-3 days to reach a new steady state, much slower than the lungs' minutes-to-hours respiratory compensation for a metabolic disturbance

Proximal tubule - reclaims ~85-90% of filtered bicarbonate via carbonic anhydrase-dependent mechanisms
Distal tubule/collecting duct - intercalated cells secrete H+ (alpha cells, acidifying) or HCO3- (beta cells, alkalinising) depending on acid-base status; ammoniagenesis in the proximal tubule generates NH4+ as the principal vehicle for excreting excess acid without further lowering urine pH
Aldosterone stimulates distal H+ secretion (alongside Na+ reabsorption/K+ secretion) - links acid-base and potassium regulation, explaining why hyperkalaemia and acidosis often coexist (e.g. Type 4 RTA, ACEi/ARB effect)

Renal contribution to acid-base status is assessed via serum bicarbonate, anion gap, and urine studies (urine pH, urine anion gap) when a primary renal tubular problem is suspected

Explains why CKD causes progressive metabolic acidosis as nephron mass and ammoniagenic capacity fall
Explains why potassium-sparing diuretics and ACEi/ARB (which reduce aldosterone effect) predispose to both hyperkalaemia and mild acidosis
Renal tubular acidosis subtypes, CKD-related acidosis, potassium-sparing diuretic effects, aldosterone physiology

Renal acid-base regulatory capacity declines progressively with nephron loss, in parallel with (but mechanistically somewhat separate from) the decline in GFR

4 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.