Chapter 59: Regulation of Body Temperature

Temperature regulation depends on a precise balance between heat generation and heat dissipation, with the hypothalamus functioning as the body's central thermoregulatory controller by integrating signals from both peripheral skin thermoreceptors and central nervous system thermosensors. Heat production occurs through several pathways including basal cellular metabolism, muscular activity, shivering-induced muscle contractions, and non-shivering thermogenesis mediated by thyroid hormones and catecholamines that increase cellular energy expenditure without muscular movement. Heat loss from the body surface occurs through four primary mechanisms: radiation of infrared energy, conduction of heat through direct contact, convection via air or fluid movement across skin, and evaporative cooling through perspiration and respiration. The hypothalamic thermostat coordinates autonomic nervous system responses including changes in skin blood flow to adjust heat transfer and activation of sweat glands for increased evaporative cooling, while also driving behavioral adaptations such as seeking warmer or cooler environments and adjusting clothing. The chapter connects normal physiology to clinical pathology by explaining fever as an upward shift in the hypothalamic temperature setpoint triggered by cytokine-mediated prostaglandin E2 signaling during infection or inflammation, contrasting this with pathological hyperthermia and heat stroke where core temperature rises dangerously despite normal setpoint regulation. Additionally, the chapter addresses cold stress responses and hypothermia as the body's temperature falls below sustainable levels, emphasizing how exercise intensity, ambient environmental extremes, and insulation properties of clothing influence overall thermal balance and survival in challenging conditions.