Functions of major physiological ions MCQs With Answer

Introduction: Functions of Major Physiological Ions MCQs with Answers (For B. Pharm)

Understanding the functions of major physiological ions is essential for B. Pharm students, bridging biochemistry, pharmacology, and clinical practice. This topic explores how sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate regulate membrane potential, action potentials, neuromuscular transmission, muscle contraction, enzyme catalysis, acid–base balance, blood coagulation, osmotic pressure, and renal handling. Learn how Na+/K+ ATPase, carbonic anhydrase, SGLT, NKCC, and hormone regulators (aldosterone, PTH, vitamin D) maintain electrolyte homeostasis and influence drug action, diuretic responses, and clinical conditions (hypo/hyperkalemia, tetany, anion gap). Master normal ranges and mechanistic insights to excel in exams and professional practice. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which ion is the principal extracellular cation in humans?

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Magnesium (Mg2+)

Correct Answer: Sodium (Na+)

Q2. Which ion is the predominant intracellular cation?

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Chloride (Cl−)

Correct Answer: Potassium (K+)

Q3. The major extracellular anion is:

• Phosphate (HPO4 2−)
• Bicarbonate (HCO3−)
• Chloride (Cl−)
• Sulfate (SO4 2−)

Correct Answer: Chloride (Cl−)

Q4. The primary extracellular buffer system is the:

• Phosphate buffer
• Bicarbonate buffer
• Protein buffer
• Ammonia buffer

Correct Answer: Bicarbonate buffer

Q5. Which ion most strongly determines extracellular fluid osmolality?

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Magnesium (Mg2+)

Correct Answer: Sodium (Na+)

Q6. Resting membrane potential in neurons and muscle is primarily set by the permeability to:

• Sodium (Na+)
• Potassium (K+)
• Calcium (Ca2+)
• Chloride (Cl−)

Correct Answer: Potassium (K+)

Q7. Neurotransmitter release at presynaptic terminals is triggered by an influx of:

• Calcium (Ca2+)
• Sodium (Na+)
• Potassium (K+)
• Chloride (Cl−)

Correct Answer: Calcium (Ca2+)

Q8. In skeletal muscle contraction, Ca2+ initiates cross-bridge cycling by binding to:

• Troponin C
• Calmodulin
• Tropomyosin
• Myosin light chain kinase

Correct Answer: Troponin C

Q9. In smooth muscle, Ca2+ activates contraction by binding to:

• Troponin C
• Calmodulin
• Titin
• Nebulin

Correct Answer: Calmodulin

Q10. Which ion is essential as “Factor IV” in the coagulation cascade?

• Magnesium (Mg2+)
• Calcium (Ca2+)
• Zinc (Zn2+)
• Iron (Fe2+/Fe3+)

Correct Answer: Calcium (Ca2+)

Q11. Inside cells, ATP predominantly exists complexed with:

• Zinc (Zn2+)
• Calcium (Ca2+)
• Magnesium (Mg2+)
• Sodium (Na+)

Correct Answer: Magnesium (Mg2+)

Q12. During the chloride shift in RBCs, when bicarbonate exits the cell, which ion enters?

• Sodium (Na+)
• Potassium (K+)
• Chloride (Cl−)
• Calcium (Ca2+)

Correct Answer: Chloride (Cl−)

Q13. The enzyme that catalyzes CO2 + H2O ⇌ H2CO3 is:

• Carbonic anhydrase
• Lactate dehydrogenase
• Acetylcholinesterase
• Aldolase

Correct Answer: Carbonic anhydrase

Q14. Carbonic anhydrase requires which metal ion as a cofactor?

• Iron (Fe2+)
• Copper (Cu2+)
• Zinc (Zn2+)
• Manganese (Mn2+)

Correct Answer: Zinc (Zn2+)

Q15. The phosphate buffer system is most effective in which location?

• Intracellular fluid and renal tubules
• Plasma only
• Interstitial fluid only
• Cerebrospinal fluid only

Correct Answer: Intracellular fluid and renal tubules

Q16. The primary inorganic component of bone (hydroxyapatite) is composed mainly of:

• Calcium and phosphate
• Sodium and chloride
• Magnesium and sulfate
• Iron and phosphate

Correct Answer: Calcium and phosphate

Q17. Each cycle of the Na+/K+ ATPase typically moves:

• 3 Na+ out, 2 K+ in
• 2 Na+ in, 3 K+ out
• 3 Na+ in, 2 K+ out
• 2 Na+ out, 2 K+ in

Correct Answer: 3 Na+ out, 2 K+ in

Q18. Aldosterone’s primary electrolyte effects in the distal nephron are:

• Decrease Na+ reabsorption and decrease K+ secretion
• Increase Na+ reabsorption and increase K+ secretion
• Increase Na+ secretion and increase K+ reabsorption
• No change in Na+ handling and decreased K+ secretion

Correct Answer: Increase Na+ reabsorption and increase K+ secretion

Q19. Parathyroid hormone (PTH) in the kidney causes:

• Decreased Ca2+ reabsorption and increased phosphate reabsorption
• Increased Ca2+ reabsorption and increased phosphate reabsorption
• Increased Ca2+ reabsorption and decreased phosphate reabsorption
• No effect on Ca2+ or phosphate handling

Correct Answer: Increased Ca2+ reabsorption and decreased phosphate reabsorption

Q20. Active vitamin D (calcitriol) primarily:

• Decreases intestinal Ca2+ and phosphate absorption
• Increases intestinal Ca2+ and phosphate absorption
• Increases renal phosphate excretion and decreases Ca2+ reabsorption
• Only affects bone resorption without affecting gut

Correct Answer: Increases intestinal Ca2+ and phosphate absorption

Q21. Hypocalcemia typically leads to:

• Reduced neuromuscular excitability
• Increased neuromuscular excitability (tetany)
• Bradycardia with shortened QT interval
• Severe hypernatremia

Correct Answer: Increased neuromuscular excitability (tetany)

Q22. A classic ECG finding in hyperkalemia is:

• Peaked T waves
• Prominent U waves
• Shortened PR interval
• Delta waves

Correct Answer: Peaked T waves

Q23. A characteristic ECG change in hypokalemia is:

• ST elevation
• Peaked T waves
• U waves
• Prolonged PR interval

Correct Answer: U waves

Q24. Normal arterial blood pH is approximately:

• 6.8–7.0
• 7.15–7.25
• 7.35–7.45
• 7.55–7.65

Correct Answer: 7.35–7.45

Q25. Normal serum sodium concentration is about:

• 115–125 mEq/L
• 125–135 mEq/L
• 135–145 mEq/L
• 145–160 mEq/L

Correct Answer: 135–145 mEq/L

Q26. The GABAA receptor increases membrane conductance to which ion?

• Sodium (Na+)
• Calcium (Ca2+)
• Chloride (Cl−)
• Potassium (K+)

Correct Answer: Chloride (Cl−)

Q27. Gastric parietal cells secrete HCl; the anion exiting apically through channels is:

• Bicarbonate (HCO3−)
• Phosphate (HPO4 2−)
• Chloride (Cl−)
• Sulfate (SO4 2−)

Correct Answer: Chloride (Cl−)

Q28. The majority of filtered bicarbonate is reabsorbed in the:

• Proximal tubule
• Thick ascending limb
• Distal convoluted tubule
• Collecting duct

Correct Answer: Proximal tubule

Q29. Loop diuretics inhibit which transporter in the thick ascending limb?

• Na+/Cl− cotransporter (NCC)
• Na+/K+/2Cl− cotransporter (NKCC2)
• Na+/H+ exchanger (NHE3)
• ENaC (epithelial Na+ channel)

Correct Answer: Na+/K+/2Cl− cotransporter (NKCC2)

Q30. A common electrolyte disturbance caused by loop diuretics is:

• Hyperkalemia
• Hypokalemia
• Hypercalcemia
• Hypermagnesemia

Correct Answer: Hypokalemia

Q31. Thiazide diuretics characteristically:

• Decrease calcium reabsorption
• Increase calcium reabsorption
• Have no effect on calcium handling
• Cause hypermagnesemia

Correct Answer: Increase calcium reabsorption

Q32. Severe magnesium deficiency typically:

• Stimulates PTH secretion causing hypercalcemia
• Suppresses PTH secretion causing hypocalcemia
• Has no effect on PTH secretion
• Only increases urinary phosphate excretion

Correct Answer: Suppresses PTH secretion causing hypocalcemia

Q33. Approximately what fraction of plasma calcium is ionized (free)?

• 10%
• 30%
• 50%
• 90%

Correct Answer: 50%

Q34. The major intracellular anion that buffers H+ is:

• Chloride (Cl−)
• Phosphate (HPO4 2−)
• Sulfate (SO4 2−)
• Iodide (I−)

Correct Answer: Phosphate (HPO4 2−)

Q35. The rapid upstroke (phase 0) of ventricular myocyte action potential is due to influx of:

• Sodium (Na+)
• Calcium (Ca2+)
• Potassium (K+)
• Chloride (Cl−)

Correct Answer: Sodium (Na+)

Q36. The plateau (phase 2) of the cardiac action potential is maintained primarily by influx of:

• Calcium (Ca2+) via L-type channels
• Sodium (Na+) via fast channels
• Chloride (Cl−) via CFTR
• Magnesium (Mg2+) via TRPM6

Correct Answer: Calcium (Ca2+) via L-type channels

Q37. Repolarization of excitable cells is mainly mediated by efflux of:

• Sodium (Na+)
• Calcium (Ca2+)
• Potassium (K+)
• Chloride (Cl−)

Correct Answer: Potassium (K+)

Q38. Insulin granule exocytosis from pancreatic β-cells is triggered directly by influx of:

• Sodium (Na+)
• Calcium (Ca2+)
• Chloride (Cl−)
• Magnesium (Mg2+)

Correct Answer: Calcium (Ca2+)

Q39. The intestinal Na+/glucose symporter (SGLT1) uses the electrochemical gradient of:

• Potassium (K+)
• Sodium (Na+)
• Calcium (Ca2+)
• Chloride (Cl−)

Correct Answer: Sodium (Na+)

Q40. The serum anion gap is commonly calculated as:

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

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

Q41. The principal titratable acid buffer in urine is:

• Ammonia (NH3/NH4+)
• Phosphate (HPO4 2−/H2PO4−)
• Bicarbonate (HCO3−)
• Lactate

Correct Answer: Phosphate (HPO4 2−/H2PO4−)

Q42. Na+/K+ ATPase activity requires which ion to complex with ATP for hydrolysis?

• Calcium (Ca2+)
• Magnesium (Mg2+)
• Sodium (Na+)
• Zinc (Zn2+)

Correct Answer: Magnesium (Mg2+)

Q43. Hyperkalemia typically shifts the resting membrane potential to be:

• More negative (hyperpolarized)
• Less negative (depolarized)
• Unchanged
• Variable with no predictable effect

Correct Answer: Less negative (depolarized)

Q44. Calcium enables vitamin K–dependent clotting factors to bind phospholipid membranes by interacting with:

• Unmodified glutamate residues
• Gamma-carboxyglutamate (Gla) residues
• Lysine residues
• Serine residues

Correct Answer: Gamma-carboxyglutamate (Gla) residues

Q45. Which ion is essential in phosphorylation reactions and energy transfer (e.g., ATP, cAMP)?

• Chloride (Cl−)
• Phosphate (PO4 3−)
• Sulfate (SO4 2−)
• Iodide (I−)

Correct Answer: Phosphate (PO4 3−)

Q46. The ion that primarily regulates extracellular fluid volume and thus blood pressure is:

• Potassium (K+)
• Sodium (Na+)
• Calcium (Ca2+)
• Magnesium (Mg2+)

Correct Answer: Sodium (Na+)

Q47. In metabolic acidosis, plasma bicarbonate concentration typically:

• Increases
• Decreases
• Remains unchanged
• Oscillates without net change

Correct Answer: Decreases

Q48. In blood, bicarbonate (HCO3−) is the conjugate base of:

• Carbonic acid (H2CO3)
• Hydrochloric acid (HCl)
• Phosphoric acid (H3PO4)
• Lactic acid

Correct Answer: Carbonic acid (H2CO3)

Q49. The CFTR gene encodes a channel that primarily conducts:

• Sodium (Na+)
• Potassium (K+)
• Chloride (Cl−)
• Calcium (Ca2+)

Correct Answer: Chloride (Cl−)

Q50. The normal serum bicarbonate (HCO3−) range in arterial blood is approximately:

• 10–14 mEq/L
• 18–22 mEq/L
• 22–26 mEq/L
• 28–32 mEq/L

Correct Answer: 22–26 mEq/L