![]() ![]() Heat loss via radiation occurs in the form of infrared rays and accounts for approximately 60% of total body heat loss. The methods by which heat is lost from the skin to the external environment occur via radiation, conduction, convection, and evaporation. īehavioral changes include increased movements, adopting a closed body position, adding clothing, and an increased appetite. There is limited capacity for thermoregulation during the first few weeks of life, especially in preterm and low birthweight infants. Additionally, immature respiratory and circulatory systems may impede proper temperature regulation. BAT is located around the kidneys, adrenal glands, scapulae, axilla, mediastinum, and spine. Newborns are more susceptible to cooling and hypothermia due to their high levels of heat loss by evaporation due to skin immaturity, elevated ratio of body surface area to weight, deficient amounts of subcutaneous adipose tissue for insulation, and poorly developed muscles. BAT is well-vascularized tissue that develops at the beginning of the third trimester, at approximately week 27 of gestation. Newborns rely on nonshivering thermogenesis to metabolize brown adipose tissue (BAT) and release energy. Though central thermoregulatory mechanisms are present at birth, they are deemed both developmentally deficient and poorly differentiated, which places the newborn, especially those that are small and premature, at risk of severe heat loss and hypothermia. The fetal hypothalamus and the thermoregulatory center of the hypothalamus form from the ventral diencephalon and are differentiated by approximately 9 to 10 weeks gestation. ![]() ![]() Interferon-gamma (IFN-gamma) is another proinflammatory cytokine that can directly cause fever via induction of IL-1 and synthesis of TNF. Prostaglandin E2 (PGE2) then stimulates the release of neurotransmitters (cAMP), increasing body temperature. These pyrogens induce cyclooxygenase 2 (COX2), which catalyzes the formation of prostaglandins (PG) from arachidonic acid. The primary endogenous pyrogens (cytokines) include interleukin-1 (IL-1) and interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha). Endogenous pyrogens originate inside the body and act on the thermoregulatory center in the hypothalamus. Exogenous pyrogens originate outside the body and induce interleukins. The febrile response is mediated by pyrogens, substances that induce fever. Numerous causes can precipitate a fever, including infection, inflammation, autoimmune processes, medications, or malignancy. These processes involve the release of immunological mediators, which trigger the thermoregulatory center of the hypothalamus, leading to an increase in the body's core temperature. The definition of 'fever' is an elevation in core body temperature above a set point, which is set by the preoptic area of the hypothalamus in the thermoregulatory center. This area then activates heat regulation mechanisms to increase or decrease body temperature and return it to baseline. The peripheral thermoreceptors are located in the skin and sense surface temperatures, while central thermoreceptors are found in the viscera, spinal cord, and hypothalamus and sense the core temperature. Variations in body temperature activate these thermoreceptors, which inform the preoptic area of the hypothalamus. The hypothalamus contains temperature sensors, which receive information via nerve cells called thermoreceptors. The body has peripheral and central thermoreceptors. This center sets the body's set point and regulates temperature homeostasis. The human body's thermostat is the hypothalamic thermoregulatory center, which, more specifically, is located in the preoptic area of the hypothalamus. Thermoregulation is the maintenance of physiologic core body temperature by balancing heat generation with heat loss. A healthy individual will have a core body temperature of 37 +/- 0.5☌ (98.6 +/- 0.9☏), the temperature range needed for the body's metabolic processes to function correctly. ![]()
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