A patient with a bacterial infection develops a fever of 39°C and begins shivering intensely. Why is the patient shivering?
AShivering is a direct immune response to bacteria, agitating tissues to improve white blood cell delivery
BPyrogens have raised the hypothalamic set point to 39°C, so the body at 37°C 'perceives' itself as too cold and activates heat-generating mechanisms
CThe infection is lowering core body temperature below 37°C, triggering the normal cold response
DThe patient is shivering because core temperature is too high and shivering helps dissipate heat
Fever is a regulated set-point elevation, not a loss of control. When pyrogens (via prostaglandin E2) raise the hypothalamic set point from 37°C to 39°C, the body at its current 37°C is below the new target — it 'feels cold.' The hypothalamus activates the same heat-generating responses (peripheral vasoconstriction, shivering) it would use on a cold day, until core temperature rises to meet the new set point.
Question 2 Multiple Choice
How do NSAIDs like ibuprofen reduce fever?
AThey directly cool blood flowing through the hypothalamus, lowering its temperature
BThey bind to and neutralize pyrogens (IL-1, IL-6) in the bloodstream before they reach the brain
CThey inhibit COX enzymes, reducing prostaglandin E2 synthesis and lowering the hypothalamic set point back toward normal
NSAIDs block cyclooxygenase (COX) enzymes, preventing the conversion of arachidonic acid to prostaglandin E2 (PGE2). Without PGE2, the hypothalamic set point falls back toward 37°C. With a lower set point, the body 'perceives' itself as too warm at fever temperature and activates heat-dissipation (sweating, vasodilation) — the fever 'breaks.' NSAIDs do not directly cool the body or neutralize cytokines.
Question 3 True / False
Fever and hyperthermia are both caused by the same mechanism — a thermoregulatory system overwhelmed by excess heat — and differ mainly in severity.
TTrue
FFalse
Answer: False
They are mechanistically distinct. In fever, the hypothalamic set point is actively reset to a higher value by pyrogens — the body is working correctly to reach its new target. In hyperthermia (e.g., heat stroke), the set point remains normal but heat gain exceeds the system's ability to dissipate — a failure of capacity. This difference matters for treatment: antipyretics work for fever but not heat stroke.
Question 4 True / False
When a fever 'breaks' after ibuprofen administration, the patient sweats and feels warm because the thermoregulatory set point has returned to normal while body temperature is still elevated above it.
TTrue
FFalse
Answer: True
After NSAIDs lower the set point back to ~37°C, the body is now above its target. The hypothalamus activates heat-dissipation responses — cutaneous vasodilation and sweating — exactly as it would in normal overheating. The patient sweats and feels warm because the normal cooling response is now directed at eliminating the excess heat that was generated during the fever.
Question 5 Short Answer
Explain why a patient with a rising fever feels cold and may shiver, even though a thermometer shows their temperature is above 37°C.
Think about your answer, then reveal below.
Model answer: Fever is a regulated set-point elevation. Pyrogens cause the hypothalamus to 'decide' that normal body temperature (37°C) is too low — the new target might be 39°C. From the hypothalamus's perspective, the current temperature is below the set point, so it activates the same responses used on a cold day: peripheral vasoconstriction (reducing heat loss) and shivering (generating heat through inefficient muscle ATP hydrolysis). The patient subjectively feels cold because the thermoregulatory system is treating the situation as cold — even though an external thermometer reads an elevated temperature. The system isn't malfunctioning; it's working correctly toward its new, higher target.
The key distinction: in fever the thermostat is reset, so behaviors appropriate to 'I am below set point' (shivering, vasoconstriction) occur even at temperatures that would be 'hot' by normal standards.