From Standard of Care
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Dependent on the balance of production and dissipation of heat.
Heat is generated by internal metabolic processes and when external temperatures exceed those of body temperature by increased muscle activity.
The body produces 40-60 kilocalories (kcal) of heat per square meter of body surface area from cellular metabolism.
As movement increases heat production does the same, so that shivering increases the rate of heat production by 2-5 times.
Heat loss from the body occurs primarily through evaporative losses via the skin and also to a lesser extent from the lungs.
Conduction and convection account for about 15% of heat loss.
Varies with anatomic site, time of day and degree of activity.
Environmental changes alter the type of heat loss that is present with cold immersion increasing conductive heat loss by 25 fold.
Core temperature regulated by interrelationship of autonomic, endocrine and behavioral responses.
Hypothalamus functions as a thermostat, controlling thermoregulatory mechanisms that balance heat production with heat loss.
Heat sensor receptors are located in the preoptic area of the anterior hypothalamus and are sensitive to increases in blood temperature and increase signal output when temperature rises above 37.1°C and decreases signal output when temperatures drop below the fixed thermal set point.
Thermal receptors that are present in the skin, spinal cord and abdomen send impulses to the hypothalamus via the spinal cord.