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FCPS Part 1 Renal and Acid-Base MCQs
Renal questions test glomerular filtration, tubular handling of sodium, potassium and water, concentrating the urine, diuretics' sites of action and the interpretation of acid–base disorders.
Below are 5 free single-best-answer questions drawn from the most frequently examined renal and acid-base concepts, each with the answer and a rationale for every option. The full bank has 55 renal and acid-base concepts, each asked several different ways.
Free renal and acid-base questions
Question 1
Gitelman syndrome results from a defective transporter in which nephron segment?
- A. Thick ascending limb
- B. Proximal convoluted tubule
- C. Collecting duct
- D. Distal convoluted tubule
- E. Thin descending limb
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Answer: D. Distal convoluted tubule
The distal convoluted tubule reabsorbs Na⁺ through the thiazide-sensitive Na⁺–Cl⁻ cotransporter, which is defective in Gitelman syndrome.
Why not the others: Proximal convoluted tubule: PTH inhibits phosphate reabsorption here. Thick ascending limb: Na⁺-K⁺-2Cl⁻ transporter, loop diuretics. Collecting duct: aldosterone and ADH act here. Thin descending limb: water permeable, no active transport.
High-yield: PTH on calcium → DCT; PTH on phosphate → PCT; thiazide and Gitelman are both DCT.
Question 2
Hormone increasing sodium reabsorption in the distal tubule and collecting duct:
- A. Cortisol
- B. Aldosterone
- C. ADH
- D. Renin
- E. ANP
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Answer: B. Aldosterone
Aldosterone increases ENaC and Na/K-ATPase activity in principal cells, so sodium is retained and potassium excreted; water follows osmotically.
Why not the others: ADH: water reabsorption. ANP: promotes natriuresis. Renin: enzyme generating angiotensin I. Cortisol: weak mineralocorticoid action. PTH: calcium handling.
High-yield: Aldosterone = sodium in, potassium out.
Question 3
Nephron segment in which ADH has its maximum effect in dehydration:
- A. Collecting duct
- B. Thin descending limb
- C. Proximal convoluted tubule
- D. Thick ascending limb
- E. Glomerulus
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Answer: A. Collecting duct
The collecting duct passes through the hypertonic medulla and its water permeability is controlled by ADH via aquaporin-2. It therefore sets final urine concentration.
Why not the others: Proximal tubule: bulk isosmotic reabsorption. Thick ascending limb: water-impermeable. Early distal tubule: thiazide site, little ADH effect. Glomerulus: filtration only.
High-yield: Where does ADH act maximally? Collecting duct; the loop builds the gradient.
Question 4
Complete bilateral ureteric obstruction raises Bowman's capsule pressure; the effect on filtration is
- A. Increased GFR
- B. Increased urine output
- C. Unchanged GFR
- D. Decreased GFR
- E. Increased renal blood flow
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Answer: D. Decreased GFR
GFR depends on glomerular capillary hydrostatic pressure minus Bowman's capsule pressure and oncotic pressure. Obstruction raises capsule pressure, while aortocaval compression in labour or haemorrhage lowers renal perfusion, so filtration falls.
Why not the others: Increased GFR: needs raised capillary pressure. Unchanged GFR: ignores the pressure change. Increased urine output: follows rising GFR. Increased renal blood flow: opposite of compression. Reduced oncotic pressure: would raise GFR.
High-yield: Labour: aortocaval compression lowers renal perfusion; left tilt relieves it.
Question 5
pH 7.10, PaCO2 60 mmHg, HCO3 18 mmol/L: acid-base disorder?
- A. Respiratory alkalosis
- B. Compensated metabolic acidosis
- C. Metabolic alkalosis with respiratory compensation
- D. Respiratory acidosis
- E. Mixed metabolic and respiratory acidosis
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Answer: E. Mixed metabolic and respiratory acidosis
In pure respiratory acidosis HCO3 should rise, and in metabolic acidosis PaCO2 should fall. Both being abnormal in the acidotic direction means two primary processes.
Why not the others: Respiratory acidosis: HCO3 would be raised, not low. Compensated metabolic acidosis: PaCO2 would be low. Respiratory alkalosis: pH would be high. Metabolic alkalosis with respiratory compensation: pH would be high.
High-yield: Acidaemia with both PaCO2 high and HCO3 low = mixed acidosis.
Keep going with renal and acid-base
Anaesgen brings every concept back on a spaced-repetition schedule timed to your exam date, as a different question each time, with full mock papers for Paper 1 and 2.
Get full access Try the 5 sample questionsHigh-yield renal and acid-base one-liners
The most-tested renal and acid-base concepts, as a clue and the answer it points to:
- PTH-Ca²⁺, Gitelman, thiazides, NCC → distal convoluted tubule.
- Distal nephron, principal cells, Na retention, K loss → aldosterone.
- ADH, aquaporin-2, principal cells and aldosterone → collecting duct.
- Ureteric obstruction, aortocaval compression, hypoperfusion → decreased GFR.
- Low pH, high PaCO2, low HCO3 → mixed metabolic and respiratory acidosis.
- Low HCO3, low PaCO2, pH slightly acidic → metabolic acidosis with respiratory compensation.
- Bone density, T-score, postmenopausal fractures → DEXA.
- Alveolar hypoventilation or flooding, raised PaCO2, low pH → drowning.
- Hypertension, low K+, alkalosis, low renin → primary hyperaldosteronism.
- Erythropoietin, amyloid with nephrosis, clear cell carcinoma/VHL → kidney.
- Diarrhoea, acetazolamide, bicarbonate loss with chloride gain → normal anion gap acidosis.
- Albumin held back, minimal change → negative charge.
- CKD hyperparathyroidism, osteoclasts, Ca2+ up, phosphate excreted → parathormone.
- Glucose, amino acids, bulk of filtered water and sodium → PCT.
- Useful solute lost in urine, glucose, amino acids → failed reabsorption.
- H+ blocks K+ channels, intensity tracks log[H+] → sour.
- Diabetic, early nephropathy, microalbuminuria → spot urine ACR.
- Collecting duct, H+-ATPase, H+/K+-ATPase, acidify urine → type A intercalated.
- Excess aldosterone, hypertension but no oedema → aldosterone escape.
- High pH, normal PaCO2, raised HCO3 → uncompensated metabolic alkalosis.
Other FCPS Part 1 subjects
AnatomyPharmacologyPathologyBiochemistry & GeneticsCardiovascularNeurophysiologyMicrobiologyHaematologyGeneral PhysiologyImmunologyEndocrineRespiratoryEmbryologyObstetrics & GynaeHistologyGI & LiverPhysicsBiostatistics
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