Which of the following best explains the sensation of intense cold and rigors observed during the rising phase of fever?

• A Peripheral vasodilation raising skin temperature
• B Activation of warm-sensitive neurons causing sweating
• C Prostaglandin E2 directly inhibiting cold-sensitive neurons
• D Elevated set-point while core temperature is still below it ✓

Explanation

During the chill phase of fever, the hypothalamic set-point is raised by prostaglandin E2, but the actual core temperature has not yet reached the new set-point. The hypothalamus interprets the current temperature as too cold, triggering vasoconstriction and shivering. Peripheral vasodilation and sweating occur during defervescence when the set-point falls, not during the chill. PGE2 raises the set-point by altering the responsiveness of thermosensitive neurons rather than selectively inhibiting cold-sensitive neurons.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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