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Vital sign temperature



Perception of and Reaction to Hot and Cold


Perception of Hot and Cold

Perception of hot and cold is by way of warm and cold receptor neurons in the hypothalamus. A change in the temperature of blood flowing through the hypothalamus activates mechanisms to stabilize body temperature. In addition, warm and cold receptors in the skin and elsewhere send messages to the hypothalamus to modify the temperature. Temperature and pain fibers of the lateral spinothalamic tract run to the thalamus, and from there via the thalamic radiation to the postcentral gyrus of the parietal lobe of the cerebral cortex. Connections exist between the postcentral gyrus, the thalamus, the reticular formation and the hypothalamus.

Reaction to Cold

Blood vessels are innervated by sympathetic fibers of the autonomic nervous system, with hypothalamic connections. When it is cold, sympathetic fibers are stimulated and vessels constrict (vasoconstriction), conserving heat The person becomes more active (i.e., pacing, arm movements). Signals are relayed down the spinal cord via the lateral columns and muscle tone is increased. As the tone rises, involuntary contraction and twitching occur (shivering). Shivering may increase body-heat to five times normal.

Reaction to Heat

When it is hot, sympathetic stimulation to vessels is inhibited and vessels widen (vasodilation). Core body heat as sweat, an ultrafiltrate of blood, moves through dilated vessels and sweat glands to skin, where evaporation takes place. Body activity decreases to prevent unnecessary heat production. When an adult is not sweating, about 700 ml of body water is lost from the skin and lungs by evaporation each day (insensible water loss). On a hot day, an active person may lose over a liter of fluid per hour by sweating. In a humid environment, poor evaporation causes body heat to remain high, contributing to heat illness.


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