Review Questions

DIRECTIONS: Each of the numbered items or incomplete statements in this section is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case.

1. Antipyretics such as aspirin effectively lower core temperature during fever, but they are not used to counteract the increase in core temperature that occurs during exercise. Which of the following best explains why it is inappropriate to use antipyretics for this purpose?

(A) The increase in core temperature during exercise stimulates metabolism via the Q10 effect, helping to support the body's increased metabolic energy demands

(B) A moderate increase in core temperature during exercise is harmless, so there is no benefit in preventing it

(C) Antipyretics are ineffective during exercise because they act on a mechanism that operates during fever, but not to a significant degree during exercise

(D) Antipyretics increase skin blood flow so as to dissipate more heat, increasing circulatory strain during exercise

(E) The increased heat production during exercise greatly exceeds the ability of antipyretics to stimulate the responses for heat loss

2. A surgical sympathectomy has completely interrupted the sympathetic nerve supply to a patient's arm. How would one expect the thermoregulatory skin blood flow and sweating responses on that arm to be affected?

Vasoconstriction Vasodilation in the Cold in the Heat Sweating

(A) Abolished Intact Intact

(B) Abolished Intact Abolished

(C) Abolished Abolished Intact

(D) Abolished Abolished Abolished

(E) Intact Abolished Abolished

3. A person resting in a constant ambient temperature is tested in the early morning at 4:00 AM, and again in the afternoon at 4:00 PM. Compared to measurements made in the morning, one would expect to find in the afternoon:

Threshold for Core Sweating Cutaneous

Temperature Threshold Vasodilation

(A) Unchanged Higher Lower

(B) Unchanged Unchanged Unchanged

(C) Higher Higher Higher

(D) Higher Unchanged Lower

(E) Lower Lower Lower

4. Compared to an unacclimatized person, one who is acclimatized to cold has

(A) Higher metabolic rate in the cold, to produce more heat

(B) Lower metabolic rate in the cold, to conserve metabolic energy

(C) Lower peripheral blood flow in the cold, to retain heat

(D) Higher blood flow in the hands and feet in the cold, to preserve their function

(E) Various combinations of the above, depending on the environment that produced acclimatization

5. Which statement best describes how the elevated core temperature during fever affects the outcome of most bacterial infections?

(A) Fever benefits the patient because most pathogens thrive best at the host's normal body temperature

(B) Fever is beneficial because it helps stimulate the immune defenses against infection

(C) Fever is harmful because the accompanying protein catabolism reduces the availability of amino acids for the immune defenses

(D) Fever is harmful because the patient's higher temperature favors growth of the bacteria responsible for infection

(E) Fever has little overall effect either way

6. A manual laborer moves in March from Canada to a hot, tropical country and becomes acclimatized by working outdoors for a month. Compared with his responses on the first few days in the tropical country, for the same activity level after acclimatization one would expect higher

(A) Core temperature

(B) Heart rate

(C) Sweating rate

(D) Sweat salt concentration

(E) Thermoregulatory set point

In questions 7 to 8, assume a 70-kg young man with the following baseline characteristics: total body water (TBW) = 40 L, extracellular fluid (ECF) volume = 15 L, plasma volume = 3 L, body surface area = 1.8 m2, plasma [Na+] = 140 mmol/L. Heat of evaporation of water = 2,425 kJ/kg = 580 kcal/kg.

7. Our subject begins an 8-hour hike in the desert carrying 5 L of water in canteens. During the hike, he sweats at a rate of 1 L/hr, his sweat [Na+] is 50 mmol/L, and he drinks all his water. After the end of his hike he rests and consumes 3 L of water. (For simplicity in calculations, assume that the plasma osmolality equals 2 times the plasma [Na+].) What are his plasma sodium concentration and ECF volume after he has replaced all the water that he lost? Plasma [Na+]

8. Our subject is bicycling on a long road with a slight upward grade. His metabolic rate (M in the heat-balance equation) is 800 W (48 kJ/min). He performs mechanical work (against gravity, friction, and wind resistance) at a rate of 140 W. Air temperature is 20°C and hc, the convective heat transfer coefficient, is 15 W/(m2^°C). Assume that his mean skin temperature is 34°C, all the sweat he secretes is evaporated, respiratory water loss can be ignored, and net heat exchange by radiation is negligible. How rapidly must he sweat to achieve heat balance? (Remember that 1 W = 1 J/sec = 60 J/min.)

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