Temperature Regulation and Fever

The temperature within the deep tissues of the body (core temperature) is normally maintained within a range of 36.0°C to 37.5°C (97.0°F to 99.5°F).12 Within this range, there are individual differences and diurnal variations; internal core temperatures reach their highest point in late afternoon and evening and their lowest point in the early morning hours (Fig. 9-11). Virtually all biochemical processes in the body are affected by changes in temperature. Metabolic processes speed up or slow down, depending on whether body temperature is rising or falling. Body temperature reflects the difference between heat production and heat loss. Body heat is generated in the tissues of the body, transferred to the skin surface by the blood, and then released into the environment surrounding the body. The thermoregulatory center in the hypothalamus functions to modify heat production and heat losses as a means of regulating body temperature. It is the core body temperature, rather than the surface temperature, that is regulated by the thermoregulatory center in the hypothalamus. This center integrates input from cold and warm thermal receptors located throughout the body and generates output responses that conserve body heat or increase its dissipation. The thermostatic set point of the thermoregulatory center is set so that the core temperature is regulated within the normal range. When body temperature begins to rise above the normal range, heat-dissipating behaviors are initiated; when the temperature falls below the normal range, heat production is increased. A core temperature greater than 41°C (105.8°F) or less than 34°C (93.2°F) usually indicates that the body’s ability to thermoregulate is impaired (Fig. 9-12). Body responses that produce, conserve, and dissipate heat are described in Table 9-2. Spinal cord injuries that transect the cord at T6 or above can seriously impair temperature regulation because the hypothalamus can no longer control skin blood flow or sweating. In addition to physiological thermoregulatory mechanisms, humans engage in voluntary behaviors to help regulate body temperature. These behaviors include the selection of proper clothing and regulation of environmental temperature through heating systems and air conditioning. Body positions that hold the extremities close to the body (e.g., huddling or holding the extremities close to the body) prevent heat loss and are commonly assumed in cold weather. 161 Chapter 9: Inflammation, Tissue Repair, and Fever