Temperature Regulation and Body Fluid Compartments MCQs

Physiology · 45 free questions with answers & explanations.

1. A 70 kg man loses 3 liters of isotonic sweat during a marathon. Which body fluid compartment will show the GREATEST absolute volume decrease?
2. During fever, the set-point of the hypothalamic thermostat is elevated. Which cytokine is the MOST potent endogenous pyrogen and what is its immediate mediator of set-point elevation at the hypothalamus?
3. A 28-year-old woman receives 1 liter of 3% NaCl IV (hypertonic saline) for severe hyponatremia. Regarding fluid compartment redistribution, which change is most accurately predicted?
4. The indicator-dilution method is used to measure body fluid compartments. Which indicator correctly measures total body water (TBW)?
5. A patient with severe hypernatraemia (serum Na+ 168 mEq/L) is being corrected with IV hypotonic fluid. Which compartmental shift predominates?
6. During fever, the set-point temperature in the hypothalamus is elevated by pyrogens. Which mechanism raises body temperature to the new set-point?
7. Tritiated water (3H2O) injected IV equilibrates with which body fluid compartment for measurement?
8. During fever induced by bacterial lipopolysaccharide (LPS), the central mechanism of temperature resetting involves:
9. A 70 kg man receives 2 liters of isotonic (0.9%) saline intravenously. After equilibration, the primary change in body fluid compartments will be:
10. Measurement of total body water (TBW) using deuterium oxide (D2O) dilution gives a result of 42L in a 70 kg man. If Evans blue dye dilution gives a plasma volume of 3.5L and hematocrit is 45%, the interstitial fluid volume is approximately:
11. A mountaineer becomes severely hypothermic (core temperature 30°C). Which thermoregulatory response is MOST likely to be ABSENT or severely impaired at this temperature?
12. A patient with syndrome of inappropriate ADH secretion (SIADH) has serum Na 118 mEq/L with normal body weight. Which body fluid compartment change BEST characterizes SIADH?
13. In exertional heat stroke, thermoregulatory failure leads to hyperthermia >41°C. Which cellular mechanism primarily underlies the multi-organ dysfunction in this condition?
14. After infusing 2 liters of isotonic (0.9%) saline rapidly, which body fluid compartment change is expected?
15. A 70 kg man is given 1 litre of isotonic saline (0.9% NaCl, osmolality 308 mOsm/kg). Immediately after equilibration, the predicted distribution of this volume across body fluid compartments is:
16. A marathon runner collapses in hot weather. Core temperature is 41.2°C, skin is hot and dry, and he is confused. Which thermoregulatory failure BEST explains the absence of sweating despite extreme hyperthermia?
17. A patient with SIADH has serum Na⁺ of 118 mEq/L. Which of the following BEST describes the shift in body fluid osmolality and compartment volumes that occurs?
18. A 70 kg man is given 2 L of hypotonic (0.45% NaCl) IV fluid rapidly. Which of the following CORRECTLY describes the shift in body fluid compartments?
19. During a marathon run in a hot environment, a runner loses 3 L of sweat (hypotonic fluid). Which combination of physiological responses is expected?
20. In heat stroke (core temperature >40°C), the failure of sweating is due to:
21. During sustained high-intensity exercise in a hot environment, a marathon runner develops hyperthermia (core temperature 40.5°C) and begins to sweat profusely. Which integrative response best describes the cardiovascular–thermoregulatory conflict that limits heat dissipation?
22. A 70 kg man is infused with 2 litres of isotonic saline (0.9% NaCl, osmolality 308 mOsm/kg). How does this affect his body fluid compartments?
23. Pyrogens such as IL-1β and IL-6 raise the thermoregulatory set-point in the preoptic area of the hypothalamus. Which is the FINAL intracellular mediator that raises the set-point by inhibiting warm-sensitive neurons?
24. The primary thermoregulatory centre is in the preoptic area of the anterior hypothalamus. Warm-sensitive neurons in this area respond to a rise in core temperature by:
25. A patient loses 2 litres of isotonic saline through a drain. Which body fluid compartment is exclusively depleted, and what is the expected effect on plasma osmolality?
26. Fever is generated when pyrogens elevate the hypothalamic thermoregulatory set-point. Which eicosanoid mediates this set-point elevation within the preoptic area?
27. Total body water (TBW) in a 70 kg adult male is approximately 60% of body weight (42 L). Two-thirds of TBW constitutes intracellular fluid (ICF). What is the approximate volume of interstitial fluid in this individual?
28. A patient receives 3 litres of isotonic (0.9%) saline intravenously. How will this expand the body fluid compartments?
29. The hypothalamic thermostat set-point for body temperature is elevated during fever by which mediator acting directly on the anterior hypothalamus?
30. In heat stroke, the core temperature exceeds 40°C and sweating fails. The failure of heat dissipation is due to:
31. A 70 kg man receives 3 L of isotonic (0.9%) saline intravenously over 4 hours. Which compartment(s) will be primarily expanded, and by how much?
32. A patient drinks 2 L of pure water rapidly. Which physiological changes will occur in steady state after maximal renal compensation?
33. During fever, which thermoregulatory response is most responsible for the sensation of feeling cold (chills) even when core body temperature is rising?
34. Malignant hyperthermia is triggered by inhalational anesthetics and succinylcholine in susceptible individuals. The primary mechanism causing hyperthermia is:
35. The Darrow-Yannet diagram is used to analyze body fluid compartment changes. A patient with primary hyperaldosteronism (Conn's syndrome) develops marked sodium and water retention. How do ECF and ICF change?
36. A 70 kg man is given 2 litres of isotonic saline (0.9% NaCl) intravenously. Assuming normal distribution, how much of the infused volume remains in the intravascular compartment after equilibration?
37. Which best describes the primary afferent pathway that conveys cold signals from peripheral thermoreceptors to the hypothalamus for thermoregulatory responses?
38. A 50 kg woman develops severe symptomatic hyponatremia (serum Na 112 mEq/L). Her estimated total body water (TBW) is 30 L. Using the sodium deficit formula, how many mEq of sodium are required to raise her serum sodium to 120 mEq/L?
39. During intense exercise in a hot environment, which thermoregulatory mechanism accounts for the greatest proportion of heat loss from the body surface?
40. A patient with SIADH has serum Na 118 mEq/L, serum osmolality 248 mOsm/kg, urine osmolality 620 mOsm/kg, urine sodium 68 mEq/L, and is euvolemic. Which renal mechanism best explains why these patients retain free water despite low plasma osmolality?
41. A 70 kg man has a total body water (TBW) of 42 L. He loses 3 L of pure water (insensible loss). What happens to his intracellular and extracellular fluid volumes?
42. In the hypothalamic thermoregulatory system, the pre-optic anterior hypothalamic area (POAH) functions as the 'thermostat'. During fever induced by IL-1, the mechanism involves:
43. The Gibbs-Donnan equilibrium across capillary walls explains the distribution of electrolytes. Which statement correctly describes this effect in plasma versus interstitial fluid?
44. A patient with severe burns over 40% BSA develops hypovolaemic shock. If 4 mL/kg/% BSA burned of normal saline is infused (Parkland formula), what volume would be given in the first 8 hours for a 75 kg patient?
45. Core body temperature is 37°C. The primary mechanism of heat loss at rest in a thermoneutral environment (25°C) is: