A mountaineer becomes severely hypothermic (core temperature 30°C). Which thermoregulatory response is MOST likely to be ABSENT or severely impaired at this temperature?

• A Peripheral vasoconstriction to conserve heat
• B Shivering thermogenesis ✓
• C Behavioral response to seek warmth
• D Reduction of sweat gland activity

Explanation

Shivering is a major source of heat production in mild to moderate hypothermia but typically ceases when core temperature falls below approximately 30-31°C, because sustained muscular activity requires adequate ATP production and neuromuscular coordination, which are severely impaired at this temperature. Peripheral vasoconstriction (option A) is an earlier reflex that may still be maintained. Behavioral thermoregulation (option C) also fails as central nervous system function deteriorates. Sweat gland activity (option D) is already suppressed at mild hypothermia.

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

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