The primary thermoregulatory centre is in the preoptic area of the anterior hypothalamus. Warm-sensitive neurons in this area respond to a rise in core temperature by:

• A Increasing firing rate and activating heat-loss mechanisms — vasodilation and sweating ✓
• B Decreasing firing rate to disinhibit posterior hypothalamic heat-production pathways
• C Releasing PGE2 locally to reset the set-point upward and trigger shivering
• D Stimulating the dorsomedial hypothalamus to increase brown adipose tissue thermogenesis

Explanation

Warm-sensitive neurons in the preoptic anterior hypothalamus (POAH) increase their firing rate in response to elevated local temperature. They activate heat-dissipation responses: cutaneous vasodilation (via inhibition of sympathetic vasomotor tone) and stimulation of eccrine sweat glands (cholinergic sympathetic innervation). Cold-sensitive neurons in the posterior hypothalamus are responsible for heat conservation (vasoconstriction) and heat production (shivering, non-shivering thermogenesis). PGE2 (option C) resets the hypothalamic set-point upward causing fever — the opposite of the physiological response to hyperthermia. Option D describes brown adipose tissue activation, which is a cold-response pathway.

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

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