Type II/ Proximal RTA (renal tubular acidosis):
- Defective HCO3 reabsorption in PCT
- Phosphaturia may occur
- Vitamin D is lost through urine, resulting in osteomalacia
- Often asymptomatic
- Rx: Oral vitamin-D.
- Inadequate reabsorption by PCT
- Everything (Glucose, amino acids, uric acid, phosphate and bicarbonate) gets excreted in urine
- Loss of bicarbonate results in type II RTA
- Loss of phosphate results in rickets and osteomalacia
- Rx: Replacement of lost substances in urine
- Expired tetracycline may damage PCT and give rise to Fanconi syndrome like condition.
Descending limb of loop of Henle
Normal function: Water reabsorption only
Thick ascending limb (TAL) of loop of Henle
Drug inhibiting NKCC2 transporter: Furosemide
- Defect in the NKCC2 transporter
- Presents at infancy
- Associated with polyhydramnios
- Severe depletion in plasma volume resulting in severe hypotension → Very high renin activity → Very high serum aldosterone level
- Defect in paracellular transport of calcium → Calciuria → Renal calculi
- Severe hypokalemia
- Worst prognosis
- Rx: Aggressive hydration.
Drug inhibiting Na-Cl transporter: Thiazide
- Defect in Na-Cl transporter of DCT
- Mild diseaes, often remains asymptomatic till 20-30 years of age
- BP of the patient is essentially normal
- Presents with abdominal cramp and ileus due to associated defect in paracellular transport of Mg (causing hypomagnesemia)
- Good prognosis
- Rx: Mg supplementation.
Principle cell: Normal function:
- Liddle syndrome:
- Inheritance: AD
- Dysregulation of the epithelial sodium channel (ENaC)
- Unregulated Na absorption → Severe hypertension → Very low renin activity → Very low serum aldosterone level
- So, there is a hyperaldosteronism-like state in presence of low aldosterone levels → It is termed as ‘pseudo-hyperaldosteronism’
- Rx: Amiloride (ENaC blocker)
- Good prognosis.
- Type IV RTA:
- There is decreased level or resistance to aldosterone
- Aldosterone increases ENaC activity
- In decreased level/ action of aldosterone, ENaC activity decreases; resulting in hyperkalemia; which is mild in severity
- Often caused by Aldosterone antagonists/ ACE-I/ ARB
- Rx: Stop the offending drugs
- Good prognosis.
Normal function: Secretion of H+
Type I/ Distal RTA:
- Failure of H+ secretion by H+ K+ ATPase pump
- Presents early with chronic severe acidemia and hypokalemia
- Urine is alkaline
- High blood acid level → Bone resorption → Short stature
- Bone resorption → Increased calcium release from bone → High serum calcium level → Polyuria & renal calculi
- High blood acid level → Intracellular acidosis → Increased citrate uptake and metabolism in the cell → Low citrate level in blood → Less amount of citrate is excreted in urine → Hypocitraturia
- Classically associated with Sjogren syndrome, may be seen with SLE & RA
- Rx: Potassium and Citrate supplementation
- Worst prognosis.
Action of ADH on collecting duct
ADH (Antidiuretic hormone) = AVP (Arginine vasopressin)
Normal function: Water absorption
Syndrome of inappropriate antidiuretic hormone secretion (SIADH):
- Inappropriately increased secretion of ADH → Enhanced water reabsorption → Volume of total body water is increased but amount of total body Na is same → Dilutional hyponatremia/ Euvolemic hyponatremia (volume is not that increased as to cause clinical edema)
- Volume expansion → Activation of atrial stretch receptors → Secretion of Atrial natriuretic peptide (ANP) → Natriuresis → High urinary Na
- Treatment of choice (TOC): Water restriction
- DOC: Vasopressin receptor antagonists (Vaptans)
- Vaptan of choice: Tolvaptan.
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