Physiological acid–base balance MCQs With Answer

Physiological acid–base balance MCQs With Answer help B. Pharm students master core concepts in clinical physiology, pathophysiology, and pharmacology. This topic covers blood pH homeostasis (7.35–7.45), bicarbonate buffer system, Henderson–Hasselbalch equation, arterial blood gases (ABG), respiratory and metabolic disturbances, renal regulation of H+ and HCO3−, anion gap, ammoniagenesis, carbonic anhydrase, and compensatory mechanisms. Understanding metabolic acidosis/alkalosis, respiratory acidosis/alkalosis, expected compensation (Winter’s formula), chloride-responsive alkalosis, and drug effects (e.g., acetazolamide, sodium bicarbonate, THAM) is essential for safe therapeutic decisions. Mastering these principles supports dosing, electrolyte correction, and interpretation of ABGs in patient care. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the normal range of arterial blood pH in healthy adults?

• 7.15–7.25
• 7.25–7.35
• 7.35–7.45
• 7.45–7.55

Correct Answer: 7.35–7.45

Q2. Which buffer system is the primary extracellular buffer maintaining physiological pH?

• Phosphate buffer system
• Bicarbonate–carbonic acid buffer system
• Hemoglobin buffer system
• Ammonia buffer system

Correct Answer: Bicarbonate–carbonic acid buffer system

Q3. In the Henderson–Hasselbalch equation for blood, which constants/terms are correctly used?

• pH = 7.0 + log([H+]/[HCO3−])
• pH = 6.1 + log([HCO3−]/(0.03 × PaCO2))
• pH = 6.8 + log(PaCO2/[HCO3−])
• pH = 6.1 + log(PaCO2/(0.03 × [HCO3−]))

Correct Answer: pH = 6.1 + log([HCO3−]/(0.03 × PaCO2))

Q4. What is the usual normal value of PaCO2 in arterial blood?

• 20 mmHg
• 30 mmHg
• 40 mmHg
• 55 mmHg

Correct Answer: 40 mmHg

Q5. The normal serum bicarbonate (HCO3−) concentration is approximately:

• 12 mEq/L
• 18 mEq/L
• 24 mEq/L
• 32 mEq/L

Correct Answer: 24 mEq/L

Q6. Hypoventilation primarily leads to which acid–base disorder?

• Metabolic acidosis
• Metabolic alkalosis
• Respiratory acidosis
• Respiratory alkalosis

Correct Answer: Respiratory acidosis

Q7. Hyperventilation primarily causes:

• Metabolic alkalosis
• Respiratory alkalosis
• Metabolic acidosis
• Mixed acidosis

Correct Answer: Respiratory alkalosis

Q8. Which renal tubular cell is chiefly responsible for H+ secretion and new bicarbonate generation?

• Proximal tubular principal cell
• Alpha-intercalated cell of the collecting duct
• Beta-intercalated cell of the collecting duct
• Macula densa cell

Correct Answer: Alpha-intercalated cell of the collecting duct

Q9. Beta-intercalated cells in the collecting duct primarily:

• Secrete H+ via H+-ATPase
• Reabsorb HCO3− via NBCe1
• Secrete HCO3− via pendrin (Cl−/HCO3− exchanger)
• Secrete NH4+ into the tubular lumen

Correct Answer: Secrete HCO3− via pendrin (Cl−/HCO3− exchanger)

Q10. Which enzyme is crucial for rapid interconversion of CO2 and H2CO3 in erythrocytes and renal tubules?

• Na+/K+-ATPase
• Carbonic anhydrase
• Adenylate cyclase
• Glutaminase

Correct Answer: Carbonic anhydrase

Q11. In acute respiratory acidosis, plasma HCO3− rises approximately how much per 10 mmHg increase in PaCO2?

• 0.5 mEq/L
• 1 mEq/L
• 3.5 mEq/L
• 5 mEq/L

Correct Answer: 1 mEq/L

Q12. In chronic respiratory acidosis, the expected HCO3− change per 10 mmHg rise in PaCO2 is about:

• 0.5 mEq/L increase
• 1 mEq/L increase
• 3–4 mEq/L increase
• 6–8 mEq/L increase

Correct Answer: 3–4 mEq/L increase

Q13. Winter’s formula estimates expected respiratory compensation in metabolic acidosis. Which is correct?

• Expected PaCO2 = 0.7 × [HCO3−] + 20 ± 5 mmHg
• Expected PaCO2 = 1.5 × [HCO3−] + 8 ± 2 mmHg
• Expected PaCO2 = 40 − 1.5 × ([HCO3−] − 24) ± 2 mmHg
• Expected PaCO2 = 0.5 × [HCO3−] + 15 ± 3 mmHg

Correct Answer: Expected PaCO2 = 1.5 × [HCO3−] + 8 ± 2 mmHg

Q14. Expected compensation for metabolic alkalosis can be approximated by:

• Expected PaCO2 ≈ 40 + 0.7 × (HCO3− − 24) ± 5 mmHg
• Expected PaCO2 ≈ 1.5 × HCO3− + 8 ± 2 mmHg
• Expected PaCO2 ≈ 20 + 0.7 × HCO3− ± 2 mmHg
• Expected PaCO2 ≈ 30 + 1.0 × (HCO3− − 24) ± 5 mmHg

Correct Answer: Expected PaCO2 ≈ 40 + 0.7 × (HCO3− − 24) ± 5 mmHg

Q15. The anion gap (without potassium) is calculated as:

• [Na+] + [K+] − ([Cl−] + [HCO3−])
• [Na+] − ([Cl−] + [HCO3−])
• [Na+] − [Cl−]
• [HCO3−] − ([Na+] + [Cl−])

Correct Answer: [Na+] − ([Cl−] + [HCO3−])

Q16. A typical normal anion gap (without potassium) is:

• 2–6 mEq/L
• 8–12 mEq/L
• 14–18 mEq/L
• 20–24 mEq/L

Correct Answer: 8–12 mEq/L

Q17. Which is a common cause of high anion gap metabolic acidosis?

• Vomiting
• Loop diuretics
• Diabetic ketoacidosis
• Hyperaldosteronism

Correct Answer: Diabetic ketoacidosis

Q18. A normal anion gap (hyperchloremic) metabolic acidosis is commonly seen in:

• Renal tubular acidosis
• Lactic acidosis
• Methanol poisoning
• Uremia

Correct Answer: Renal tubular acidosis

Q19. Which transport process traps ammonium (NH4+) in the collecting duct to aid acid excretion?

• NH4+ substitution for K+ on ROMK channels
• NH3 diffusion and protonation to NH4+ in acidic lumen
• Direct NH4+ active secretion by H+-ATPase
• NH4+/Cl− cotransport into lumen

Correct Answer: NH3 diffusion and protonation to NH4+ in acidic lumen

Q20. Which statement about acetazolamide is correct regarding acid–base balance?

• It inhibits aldosterone, causing metabolic alkalosis
• It inhibits carbonic anhydrase, causing metabolic acidosis
• It stimulates H+ secretion, causing metabolic alkalosis
• It increases ammoniagenesis, causing metabolic alkalosis

Correct Answer: It inhibits carbonic anhydrase, causing metabolic acidosis

Q21. In distal (type 1) renal tubular acidosis, a characteristic finding is:

• Low urine pH (<5.5) during acidosis
• High urine pH (>5.5) despite systemic acidosis
• Hyperkalemia with decreased NH4+ excretion
• Marked glycosuria without hyperglycemia

Correct Answer: High urine pH (>5.5) despite systemic acidosis

Q22. Type 4 renal tubular acidosis is most closely associated with:

• Hypoaldosteronism and hyperkalemia
• Hyperaldosteronism and hypokalemia
• Carbonic anhydrase deficiency and hypokalemia
• Fanconi syndrome and hypocalcemia

Correct Answer: Hypoaldosteronism and hyperkalemia

Q23. Which mnemonic best represents modern causes of high anion gap metabolic acidosis?

• MUDPILES
• GOLDMARK
• RIFLE
• RUSH ABC

Correct Answer: GOLDMARK

Q24. The chloride shift (Hamburger phenomenon) refers to:

• Exchange of H+ for K+ across skeletal muscle
• Movement of Cl− into RBCs as HCO3− exits
• Secretion of Cl− in the renal distal tubule
• Cl−/HCO3− exchange in gastric parietal cells

Correct Answer: Movement of Cl− into RBCs as HCO3− exits

Q25. Which describes the Bohr effect in hemoglobin physiology?

• O2 binding increases CO2 affinity
• Increased H+ and CO2 reduce hemoglobin’s O2 affinity
• CO binds to reduce O2 delivery via methemoglobin formation
• 2,3-BPG increases hemoglobin’s O2 affinity

Correct Answer: Increased H+ and CO2 reduce hemoglobin’s O2 affinity

Q26. Deoxygenated hemoglobin is a better buffer than oxygenated hemoglobin because:

• It cannot bind protons
• It has more available imidazole groups to accept H+
• It increases blood chloride content
• It lowers 2,3-BPG levels

Correct Answer: It has more available imidazole groups to accept H+

Q27. Which of the following is considered a volatile acid in physiology?

• Lactic acid
• Sulfuric acid
• Phosphoric acid
• Carbon dioxide

Correct Answer: Carbon dioxide

Q28. The relationship between alveolar ventilation and PaCO2 is best described as:

• Directly proportional
• Inversely proportional
• Unrelated
• Logarithmically related

Correct Answer: Inversely proportional

Q29. Which intracellular buffer systems are most important?

• Bicarbonate only
• Phosphate and proteins (including hemoglobin)
• Ammonia exclusively
• Albumin only

Correct Answer: Phosphate and proteins (including hemoglobin)

Q30. The pKa of the bicarbonate buffer system at body temperature is approximately:

• 5.8
• 6.1
• 6.8
• 7.4

Correct Answer: 6.1

Q31. Which acid–base pattern is typical in salicylate (aspirin) poisoning?

• Early metabolic acidosis only
• Early respiratory alkalosis followed by anion gap metabolic acidosis
• Respiratory acidosis followed by metabolic alkalosis
• Pure metabolic alkalosis

Correct Answer: Early respiratory alkalosis followed by anion gap metabolic acidosis

Q32. Persistent vomiting most commonly causes which disorder?

• High anion gap metabolic acidosis
• Normal anion gap metabolic acidosis
• Metabolic alkalosis (chloride-responsive)
• Respiratory alkalosis

Correct Answer: Metabolic alkalosis (chloride-responsive)

Q33. Loop and thiazide diuretics can cause metabolic alkalosis primarily by:

• Increasing fixed acid production
• Volume contraction increasing HCO3− reabsorption
• Inhibiting carbonic anhydrase
• Reducing aldosterone action

Correct Answer: Volume contraction increasing HCO3− reabsorption

Q34. Chloride-resistant metabolic alkalosis is classically associated with:

• Gastric fluid loss
• Primary hyperaldosteronism
• Acetazolamide therapy
• Diarrhea

Correct Answer: Primary hyperaldosteronism

Q35. Regarding compensation in simple acid–base disorders:

• Compensation often overshoots and overcorrects pH
• Compensation never changes PaCO2
• Compensation aims to minimize pH change but rarely normalizes pH
• Compensation corrects pH to exactly 7.40

Correct Answer: Compensation aims to minimize pH change but rarely normalizes pH

Q36. A rule of thumb: in acute respiratory acidosis, for each 10 mmHg rise in PaCO2, pH falls by approximately:

• 0.02
• 0.03
• 0.08
• 0.12

Correct Answer: 0.08

Q37. Which step is most appropriate first when interpreting an ABG?

• Calculate delta gap
• Assess pH to determine acidemia or alkalemia
• Calculate base excess
• Check oxygen saturation

Correct Answer: Assess pH to determine acidemia or alkalemia

Q38. Base excess is best defined as:

• The amount of base required to raise pH to 7.60
• The amount of acid needed to titrate blood to pH 7.40 at PaCO2 40 mmHg
• The difference between Na+ and Cl−
• Serum bicarbonate concentration

Correct Answer: The amount of acid needed to titrate blood to pH 7.40 at PaCO2 40 mmHg

Q39. In lactic acidosis due to tissue hypoxia, the primary mechanism is:

• Decreased glycolysis
• Anaerobic metabolism increasing L-lactate production
• Increased renal excretion of lactate
• Enhanced oxidative phosphorylation

Correct Answer: Anaerobic metabolism increasing L-lactate production

Q40. Which statement about albumin and acid–base is correct (Stewart perspective)?

• Albumin is a strong base and raises pH when low
• Albumin is a weak acid; hypoalbuminemia tends to alkalinize
• Albumin has no effect on pH
• Albumin directly changes PaCO2

Correct Answer: Albumin is a weak acid; hypoalbuminemia tends to alkalinize

Q41. Strong ion difference (SID) is best described as:

• Total weak acids minus strong cations
• Difference between sums of strong cations and strong anions
• Sum of bicarbonate and carbonic acid
• Anion gap corrected for albumin

Correct Answer: Difference between sums of strong cations and strong anions

Q42. Which therapy can directly raise serum bicarbonate but risks sodium load and paradoxical CNS acidosis?

• Tromethamine (THAM)
• Sodium bicarbonate
• Acetazolamide
• Ammonium chloride

Correct Answer: Sodium bicarbonate

Q43. THAM (tromethamine) as a buffer is relatively contraindicated in:

• Respiratory alkalosis
• Renal failure due to renal excretion requirement
• Metabolic alkalosis
• Acute hyperkalemia

Correct Answer: Renal failure due to renal excretion requirement

Q44. Which statement about H+/K+ shifts is correct?

• Acidemia generally causes intracellular K+ shift leading to hypokalemia
• Acidemia tends to cause hyperkalemia via H+/K+ exchange in mineral acidosis
• Alkalemia increases extracellular K+ causing hyperkalemia
• Organic acidosis causes marked hyperkalemia

Correct Answer: Acidemia tends to cause hyperkalemia via H+/K+ exchange in mineral acidosis

Q45. Hypocapnia (low PaCO2) has which effect on cerebral blood flow?

• Increases cerebral blood flow
• Decreases cerebral blood flow
• No effect
• First increases, then decreases

Correct Answer: Decreases cerebral blood flow

Q46. Which pair correctly matches primary disorder and typical compensation?

• Metabolic acidosis: increase in PaCO2
• Metabolic alkalosis: decrease in PaCO2
• Respiratory acidosis: decrease in HCO3−
• Respiratory alkalosis: increase in HCO3−

Correct Answer: Metabolic alkalosis: decrease in PaCO2

Q47. Which acid load is mainly produced from metabolism of sulfur-containing amino acids?

• Carbonic acid
• Phosphoric acid
• Sulfuric acid
• Lactic acid

Correct Answer: Sulfuric acid

Q48. In mixed acid–base disorders, which finding most strongly suggests a mixed process?

• Compensation exactly matches predicted formulas
• PaCO2 or HCO3− deviates beyond expected compensation ranges
• Normal anion gap in acidosis
• Normal pH with minor PaCO2 change

Correct Answer: PaCO2 or HCO3− deviates beyond expected compensation ranges

Q49. What is the expected HCO3− change in acute respiratory alkalosis per 10 mmHg fall in PaCO2?

• Decrease by ~2 mEq/L
• Decrease by ~4–5 mEq/L
• Increase by ~2 mEq/L
• No change

Correct Answer: Decrease by ~2 mEq/L

Q50. Which statement about ABG evaluation sequence is most appropriate?

• Check PaCO2, then assume the disorder
• Assess pH, determine primary process, calculate anion gap, then assess compensation
• Calculate base excess first, then ignore PaCO2
• Evaluate electrolytes only; blood gases are unnecessary

Correct Answer: Assess pH, determine primary process, calculate anion gap, then assess compensation

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com