Body temperature

Dependent on the balance of production and dissipation of heat.

Normal body temperature was established as 37°C (98.6°F).

Normal body temperature was established as 37°C (98.6°F).

Since the 19 century human bodies have gradually become cooler and population-based data show temperatures have been steadily declining a rate of approximately .03 to .5°C per decade, currently the normal temperature range is 36.3 to 36.5°C.

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.

Preoptic area and the anterior hypothalamus play key roles in thermal homeostasis.

Cytokine induction of temperature such as interleukin-1 ,and interleukin-6 by pathogens or inflammatory stimuli triggers prostaglandin E2 production by brain endothelial cells, which resets the thermoregulatory setpoint in the preoptic area, eliciting a febrile response.

The preoptic area also controls cutaneous vasoconstriction, non-shivering thermogenesis in brown adipose tissue and shivering thermogenesis in skeletal muscles.

Thermal receptors that are present in the skin, spinal cord and abdomen send impulses to the hypothalamus via the spinal cord.

Fever related anorexia is mediated by prostaglandin.

Counterregulatory cytokines such as interleukin 10 and other anti-pyretic mediators function as inhibitors of fever and prevent detrimental elevations of temperature.

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