A marathon runner collapses in hot weather. Core temperature is 41.2°C, skin is hot and dry, and he is confused. Which thermoregulatory failure BEST explains the absence of sweating despite extreme hyperthermia?

• A Exhaustion of sweat gland capacity from prolonged maximal sweating, leading to sweat gland fatigue ✓
• B Negative feedback inhibition of anterior hypothalamic warm-sensitive neurons by elevated catecholamines
• C Cutaneous vasoconstriction shunting blood away from sweat glands
• D Loss of acetylcholine sensitivity at sweat gland muscarinic receptors due to heat denaturation

Explanation

Classic exertional heat stroke presents with hot, dry skin due to sudomotor failure after sustained maximal sweating. Sweat gland fatigue occurs when prolonged continuous eccrine sweating depletes the glands' ability to produce sweat — the ductal cells become unable to secrete despite ongoing hypothalamic signals. Additionally, severe dehydration reduces sweat rate. The anterior hypothalamus (preoptic area) warm-sensitive neurons remain active during heat stroke, so option B is incorrect. Cutaneous vasodilation (not vasoconstriction) is expected in heat stroke, ruling out option C. Option D (receptor denaturation) does not occur at physiological temperatures reached in heat stroke.

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

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Written and medically reviewed by the StethoPrep medical team.