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.
Images used in this webpage to describe the topic(s) properly to the audience might be copyrighted under other person(s) or publishing house(s) or respective company. We have solely used them for non-commercial educational purpose only; not intended to any unfair means or copyright violation. Still if you want any image(s) to be removed from this webpage, please leave a message to email@example.com with proper evidence of authorization (link to original work and allegedly infringing url) and we will not hesitate to process your request as early as possible and delete the respective image(s). Thank you for cooperating with us.