In heat stroke, the core temperature exceeds 40°C and sweating fails. The failure of heat dissipation is due to:

• A Elevated set-point in the anterior hypothalamus
• B Increased metabolic heat production from thyroid storm
• C Cutaneous vasoconstriction mediated by the sympathetic nervous system
• D Failure of thermoregulatory mechanisms despite a normal set-point (hyperthermia, not fever) ✓

Explanation

Heat stroke is a true hyperthermia — the hypothalamic set-point remains normal, but the body's heat-dissipation mechanisms (sweating, cutaneous vasodilation) are overwhelmed or fail. This is distinct from fever, where the set-point is actively elevated. The skin is typically hot and dry in classic heat stroke (anhidrosis), reflecting failure of the sweating effector mechanism. The pathophysiology includes direct thermal cellular injury, cytokine release, and rhabdomyolysis.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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