During fever, which mechanism raises the thermoregulatory set point?

During fever, which mechanism raises the thermoregulatory set point?

• A. Pyrogenic signaling increases the hypothalamic set point.
• B. Decreased metabolic activity lowers the set point.
• C. A rising ambient temperature artificially increases body temperature.
• D. An increased sweat rate lowers the set point.

Answer: (B)

Fever works by raising the hypothalamic thermostat. Pyrogenic signals, such as inflammatory cytokines, stimulate the production of prostaglandin E2 in the hypothalamus, which increases the thermoregulatory set point. With a higher set point, the body interprets itself as too cold and activates heat-generating and heat-conserving responses—shivering, increased metabolism, and vasoconstriction—to raise core temperature toward that new target. When pyrogen levels fall and the set point returns to normal, heat-loss mechanisms like sweating and vasodilation bring temperature back down. The idea that decreased metabolism lowers the set point isn’t consistent with fever, which involves increasing heat production to meet a higher target. Ambient temperature doesn’t by itself raise the internal set point; it influences heat loss or gain but doesn’t reprogram the brain’s thermostat. Sweating promotes cooling, not raising the set point, so it doesn’t explain fever’s mechanism either.

Fever works by raising the hypothalamic thermostat. Pyrogenic signals, such as inflammatory cytokines, stimulate the production of prostaglandin E2 in the hypothalamus, which increases the thermoregulatory set point. With a higher set point, the body interprets itself as too cold and activates heat-generating and heat-conserving responses—shivering, increased metabolism, and vasoconstriction—to raise core temperature toward that new target. When pyrogen levels fall and the set point returns to normal, heat-loss mechanisms like sweating and vasodilation bring temperature back down.

The idea that decreased metabolism lowers the set point isn’t consistent with fever, which involves increasing heat production to meet a higher target. Ambient temperature doesn’t by itself raise the internal set point; it influences heat loss or gain but doesn’t reprogram the brain’s thermostat. Sweating promotes cooling, not raising the set point, so it doesn’t explain fever’s mechanism either.