Composition and functions of body fluids MCQs With Answer

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Composition and functions of body fluids MCQs With Answer is a focused resource for B. Pharm students to master body fluid physiology, composition, and clinical correlations. This concise question set emphasizes total body water distribution, intracellular and extracellular compartments, key electrolytes (Na+, K+, Ca2+, Cl-, HCO3-), plasma proteins, oncotic and hydrostatic pressures, buffer systems, osmolality, and hormonal regulation (ADH, aldosterone, ANP). Questions integrate renal handling, acid–base balance, and common clinical scenarios such as edema, dehydration, hyponatremia, and hyperkalemia to bridge pharmacology and pathophysiology. Answer keys include concise explanations to aid revision and clinical application. Keywords: body fluids, plasma, interstitial fluid, intracellular fluid, electrolytes, pH, osmosis, oncotic pressure, buffer systems. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What approximate percentage of total body weight is water in a healthy young adult male?

  • 30%
  • 40%
  • 60%
  • 75%

Correct Answer: 60%

Q2. Which ion is the principal intracellular cation responsible for resting membrane potential?

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

Correct Answer: Potassium (K+)

Q3. Which ion is the major extracellular cation that largely determines serum osmolality?

  • Potassium (K+)
  • Sodium (Na+)
  • Magnesium (Mg2+)
  • Phosphate (PO4 3-)

Correct Answer: Sodium (Na+)

Q4. Normal plasma osmolality in adults is closest to which value?

  • 200–240 mOsm/kg
  • 275–295 mOsm/kg
  • 320–340 mOsm/kg
  • 360–380 mOsm/kg

Correct Answer: 275–295 mOsm/kg

Q5. Which plasma protein is primarily responsible for maintaining oncotic (colloid osmotic) pressure?

  • Fibrinogen
  • Globulins
  • Albumin
  • C-reactive protein

Correct Answer: Albumin

Q6. Which force favors filtration of fluid out of the capillary at the arterial end according to Starling’s forces?

  • Capillary oncotic pressure
  • Interstitial hydrostatic pressure
  • Capillary hydrostatic pressure
  • Lymphatic oncotic pressure

Correct Answer: Capillary hydrostatic pressure

Q7. Which buffer system is the primary extracellular buffer for regulating blood pH?

  • Hemoglobin buffer system
  • Phosphate buffer system
  • Bicarbonate (HCO3-/CO2) buffer system
  • Protein side-chain buffers

Correct Answer: Bicarbonate (HCO3-/CO2) buffer system

Q8. Which compartment contains the largest proportion of total body water?

  • Plasma
  • Interstitial fluid
  • Intracellular fluid
  • Transcellular fluid

Correct Answer: Intracellular fluid

Q9. Which of the following best describes serum compared with plasma?

  • Serum contains clotting factors while plasma does not
  • Serum is plasma without fibrinogen and clotting proteins
  • Serum has more albumin than plasma
  • Serum contains red blood cells

Correct Answer: Serum is plasma without fibrinogen and clotting proteins

Q10. Transcellular fluid includes which of the following?

  • Plasma and interstitial fluid
  • Cerebrospinal fluid and synovial fluid
  • Intracellular water in muscle only
  • Lymph and interstitial fluid combined

Correct Answer: Cerebrospinal fluid and synovial fluid

Q11. Antidiuretic hormone (ADH, vasopressin) primarily acts to increase water reabsorption in which nephron segment?

  • Proximal convoluted tubule
  • Thick ascending limb of loop of Henle
  • Distal convoluted tubule
  • Collecting duct

Correct Answer: Collecting duct

Q12. Aldosterone increases sodium reabsorption by upregulating which membrane transporter/action in principal cells?

  • Na+/K+ ATPase and apical ENaC channels
  • Apical Na+/H+ exchanger only
  • Basolateral aquaporin expression
  • Na+-glucose cotransporter

Correct Answer: Na+/K+ ATPase and apical ENaC channels

Q13. Atrial natriuretic peptide (ANP) primarily causes which effect?

  • Increased aldosterone secretion
  • Renal sodium and water retention
  • Vasodilation and increased natriuresis
  • Increased ADH release

Correct Answer: Vasodilation and increased natriuresis

Q14. Which anion is the main extracellular anion that follows sodium to maintain electroneutrality?

  • Bicarbonate (HCO3-)
  • Phosphate (PO4 3-)
  • Chloride (Cl-)
  • Sulfate (SO4 2-)

Correct Answer: Chloride (Cl-)

Q15. Which buffer system is particularly important inside cells and in renal tubular fluid?

  • Bicarbonate buffer
  • Hemoglobin buffer
  • Phosphate buffer
  • Plasma protein buffer

Correct Answer: Phosphate buffer

Q16. Which clinical feature is most characteristic of acute hyponatremia?

  • Hyperreflexia without neurological symptoms
  • Severe muscle hypertrophy
  • Cerebral edema with headache, nausea, seizures
  • Dry mucous membranes only

Correct Answer: Cerebral edema with headache, nausea, seizures

Q17. Which formula gives an approximate plasma osmolality (mOsm/kg)?

  • 2 × [K+] + glucose/18 + BUN/2.8
  • 2 × [Na+] + glucose/18 + BUN/2.8
  • [Na+] + [K+] + [Cl-]
  • Glucose × BUN × 2

Correct Answer: 2 × [Na+] + glucose/18 + BUN/2.8

Q18. Which change most commonly leads to formation of peripheral edema?

  • Increased plasma oncotic pressure
  • Decreased capillary hydrostatic pressure
  • Increased capillary hydrostatic pressure or decreased plasma oncotic pressure
  • Excessive lymphatic drainage

Correct Answer: Increased capillary hydrostatic pressure or decreased plasma oncotic pressure

Q19. Metabolic acidosis typically causes which shift of potassium between compartments?

  • Potassium shifts into cells causing hypokalemia
  • Potassium shifts out of cells causing hyperkalemia
  • No change in potassium distribution
  • Only renal potassium excretion increases

Correct Answer: Potassium shifts out of cells causing hyperkalemia

Q20. Which intervention would acutely increase plasma oncotic pressure?

  • Infusion of normal saline (0.9% NaCl)
  • Infusion of isotonic dextrose solution
  • Administration of intravenous albumin
  • Giving a loop diuretic

Correct Answer: Administration of intravenous albumin

Q21. Where is the greatest fraction of filtered sodium reabsorbed in the nephron?

  • Proximal convoluted tubule
  • Thick ascending limb of loop of Henle
  • Distal convoluted tubule
  • Collecting duct

Correct Answer: Proximal convoluted tubule

Q22. Which condition increases ADH secretion and promotes free water retention?

  • Hypernatremia and increased plasma osmolality
  • Hypovolemia and low plasma osmolality
  • Volume overload with low osmolality
  • High atrial pressure due to hypervolemia

Correct Answer: Hypernatremia and increased plasma osmolality

Q23. Approximate normal intracellular potassium concentration is closest to:

  • 4 mEq/L
  • 20 mEq/L
  • 140 mEq/L
  • 300 mEq/L

Correct Answer: 140 mEq/L

Q24. Normal serum sodium concentration range is best described as:

  • 90–110 mEq/L
  • 115–125 mEq/L
  • 135–145 mEq/L
  • 150–165 mEq/L

Correct Answer: 135–145 mEq/L

Q25. Which buffer system provides the fastest initial defense against acute pH changes?

  • Respiratory CO2 control
  • Renal bicarbonate regeneration
  • Intracellular and extracellular chemical buffers (e.g., bicarbonate, proteins)
  • Bone buffering over days to weeks

Correct Answer: Intracellular and extracellular chemical buffers (e.g., bicarbonate, proteins)

Q26. Oncotic pressure specifically refers to which of the following?

  • Hydrostatic pressure generated by blood flow
  • Osmotic pressure due to plasma proteins
  • Osmotic pressure due to small ions like Na+
  • Pressure of interstitial fluid on lymphatics

Correct Answer: Osmotic pressure due to plasma proteins

Q27. Which laboratory finding differentiates dehydration due to water loss from dehydration due to salt loss?

  • Serum sodium decreases in pure water loss
  • Serum sodium increases in water loss and decreases in salt loss
  • Serum potassium is the sole marker
  • Hematocrit remains unchanged in both

Correct Answer: Serum sodium increases in water loss and decreases in salt loss

Q28. Which intravenous fluid is considered isotonic and commonly used for volume resuscitation?

  • 0.45% NaCl (half-normal saline)
  • 0.9% NaCl (normal saline)
  • 3% NaCl (hypertonic saline)
  • 5% dextrose in water (D5W) after infusion

Correct Answer: 0.9% NaCl (normal saline)

Q29. In which clinical scenario is plasma oncotic pressure most likely decreased, promoting edema?

  • Severe hypoalbuminemia from nephrotic syndrome
  • Congestive heart failure with increased capillary hydrostatic pressure
  • Lymphatic obstruction after surgery
  • Hyperproteinemia due to multiple myeloma

Correct Answer: Severe hypoalbuminemia from nephrotic syndrome

Q30. Which mechanism most directly drives water movement across cell membranes between intracellular and extracellular compartments?

  • Active transport via ATP-dependent water pumps
  • Diffusion of water through lipid bilayer only
  • Osmosis driven by osmotic gradients (solute concentration differences)
  • Bulk flow driven by hydrostatic pressure only

Correct Answer: Osmosis driven by osmotic gradients (solute concentration differences)

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