Chapter 14: Observations
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Anatomy and physiology
The core body temperature is set and closely regulated by the thermoregulatory centre of the hypothalamus in the brain. The normal range of 36.0–37.5°C is optimal for cell metabolic activity (Tortora and Derrickson [199]).
All tissues produce heat as a result of cell metabolism, and this is increased by exercise and activity (Marieb and Hoehn [110]). Humans have the ability through homeostasis to maintain a constant core temperature despite environmental changes (Tortora and Derrickson [199]). The body's core (arterial blood) generally has the highest temperature while the skin has the coolest (Marieb and Hoehn [110], Marieb and Keller [111]).
The hypothalamus contains a group of neurones in the anterior and posterior portions, referred to as the ‘preoptic area’, that work as a thermostat (Figure 14.37) (Tortora and Derrickson [199]). The body requires stability of its temperature to produce an optimum environment for biochemical and enzymic reactions to maintain cellular function (Tortora and Derrickson [199]). Body temperature above or below the normal range affects total body function (Marieb and Hoehn [110]). A temperature above 41°C can cause convulsions and a temperature of 43°C renders life unsustainable (Wilkinson et al. [215]).
Figure 14.37 Mechanisms of body temperature regulation.
Heat is a by‐product of the metabolic reactions of all cells in the body, especially those of the muscles and liver (Waugh and Grant [207]). Heat loss is achieved through the skin by the processes of radiation, convection, conduction and evaporation (Marieb and Hoehn [110]). Various factors cause fluctuations of temperature:
- The body's circadian rhythms cause daily fluctuations; however, body temperature is usually higher in the evening than in the morning (Marieb and Hoehn [110]). Differences can reach 1.5°C.
- Ovulation can elevate the body's temperature as it influences the basal metabolic rate (Tortora and Derrickson [199]).
- Exercise and eating cause elevations in temperature (Marieb and Hoehn [110]).
- Age affects a person's response to environmental change as the core temperature of healthy people over 65 years is lower than that of younger people, resulting in limitations to their tolerance of thermal extremes (Waugh and Grant [207]). This is due to the deterioration of thermoregulatory functions with advancing age (Blatteis [20], Greaney et al. [76]). However, thermoregulation is also inadequate in newborns, and especially in low‐birth‐weight babies and those delivered by caesarean section (Vilinsky and Sheridan [203]).
