Chapter 28: Regulation of Body Temperature & Thermoregulation

Regulation of Body Temperature & Thermoregulation begins by distinguishing the body's warm internal core from the variable outer shell, explaining the physics of heat transfer including conduction, convection, radiation, and the crucial role of evaporation. The text breaks down the heat balance equation, illustrating how metabolic rate, work, and environmental exchange determine heat storage, while also defining the Q10 effect regarding temperature-dependent reaction rates. A major focus is placed on the physiologic control systems, specifically the integration of thermal information by the preoptic area of the anterior hypothalamus, which processes inputs from peripheral TRP ion channels and central sensors to regulate effector responses. The chapter elaborates on heat-dissipating mechanisms such as active sympathetic cutaneous vasodilation and eccrine sweating, alongside heat-conserving responses like adrenergic vasoconstriction, countercurrent heat exchange, and shivering thermogenesis. Significant attention is given to the distinction between the thermoregulatory set point and load error, using this framework to differentiate fever—mediated by pyrogens, cytokines, and prostaglandin E2 elevating the set point—from exercise hyperthermia, which represents a sustained load error. The physiological strain of exercise in the heat is explored, including cardiovascular drift, splanchnic vasoconstriction, and the competition between skin and muscle for blood flow. The process of acclimatization is detailed, describing adaptations such as expanded plasma volume, lower heart rate, and aldosterone-mediated salt conservation in sweat. Finally, the chapter covers clinical pathophysiology, including the progression from heat syncope and exhaustion to life-threatening heatstroke, the genetic basis of malignant hyperthermia via ryanodine receptor mutations, and the systemic effects of accidental and therapeutic hypothermia on cardiac and neural function.