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Advances in Physiology Education Sep 2015Thermoregulation is the maintenance of a relatively constant core body temperature. Humans normally maintain a body temperature at 37°C, and maintenance of this... (Review)
Review
Thermoregulation is the maintenance of a relatively constant core body temperature. Humans normally maintain a body temperature at 37°C, and maintenance of this relatively high temperature is critical to human survival. This concept is so important that control of thermoregulation is often the principal example cited when teaching physiological homeostasis. A basic understanding of the processes underpinning temperature regulation is necessary for all undergraduate students studying biology and biology-related disciplines, and a thorough understanding is necessary for those students in clinical training. Our aim in this review is to broadly present the thermoregulatory process taking into account current advances in this area. First, we summarize the basic concepts of thermoregulation and subsequently assess the physiological responses to heat and cold stress, including vasodilation and vasoconstriction, sweating, nonshivering thermogenesis, piloerection, shivering, and altered behavior. Current research is presented concerning the body's detection of thermal challenge, peripheral and central thermoregulatory control mechanisms, including brown adipose tissue in adult humans and temperature transduction by the relatively recently discovered transient receptor potential channels. Finally, we present an updated understanding of the neuroanatomic circuitry supporting thermoregulation.
Topics: Adaptation, Physiological; Adult; Body Temperature; Body Temperature Regulation; Female; Fever; Humans; Hypothermia; Male; Sensitivity and Specificity; Shivering; Skin Temperature; Sweating; Thermoreceptors; Thermosensing
PubMed: 26330029
DOI: 10.1152/advan.00126.2014 -
Physiological Reviews Oct 2022The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is... (Review)
Review
The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.
Topics: Body Temperature Regulation; Heat Stress Disorders; Heat-Shock Response; Humans; Sweating; Temperature
PubMed: 35679471
DOI: 10.1152/physrev.00047.2021 -
Anesthesiology Aug 2008Most clinically available thermometers accurately report the temperature of whatever tissue is being measured. The difficulty is that no reliably... (Review)
Review
Most clinically available thermometers accurately report the temperature of whatever tissue is being measured. The difficulty is that no reliably core-temperature-measuring sites are completely noninvasive and easy to use-especially in patients not undergoing general anesthesia. Nonetheless, temperature can be reliably measured in most patients. Body temperature should be measured in patients undergoing general anesthesia exceeding 30 min in duration and in patients undergoing major operations during neuraxial anesthesia. Core body temperature is normally tightly regulated. All general anesthetics produce a profound dose-dependent reduction in the core temperature, triggering cold defenses, including arteriovenous shunt vasoconstriction and shivering. Anesthetic-induced impairment of normal thermoregulatory control, with the resulting core-to-peripheral redistribution of body heat, is the primary cause of hypothermia in most patients. Neuraxial anesthesia also impairs thermoregulatory control, although to a lesser extent than does general anesthesia. Prolonged epidural analgesia is associated with hyperthermia whose cause remains unknown.
Topics: Anesthesia, General; Body Temperature; Body Temperature Regulation; Humans; Hypothermia; Monitoring, Intraoperative; Shivering; Skin Temperature; Sweating
PubMed: 18648241
DOI: 10.1097/ALN.0b013e31817f6d76 -
Neuron Apr 2018The regulation of body temperature is one of the most critical functions of the nervous system. Here we review our current understanding of thermoregulation in mammals.... (Review)
Review
The regulation of body temperature is one of the most critical functions of the nervous system. Here we review our current understanding of thermoregulation in mammals. We outline the molecules and cells that measure body temperature in the periphery, the neural pathways that communicate this information to the brain, and the central circuits that coordinate the homeostatic response. We also discuss some of the key unresolved issues in this field, including the following: the role of temperature sensing in the brain, the molecular identity of the warm sensor, the central representation of the labeled line for cold, and the neural substrates of thermoregulatory behavior. We suggest that approaches for molecularly defined circuit analysis will provide new insight into these topics in the near future.
Topics: Animals; Body Temperature; Body Temperature Regulation; Brain; Homeostasis; Humans; Neural Pathways; Thermosensing
PubMed: 29621489
DOI: 10.1016/j.neuron.2018.02.022 -
Neuroscience Letters Mar 2019Maintenance of mammalian core body temperature within a narrow range is a fundamental homeostatic process to optimize cellular and tissue function, and to improve... (Review)
Review
Maintenance of mammalian core body temperature within a narrow range is a fundamental homeostatic process to optimize cellular and tissue function, and to improve survival in adverse thermal environments. Body temperature is maintained during a broad range of environmental and physiological challenges by central nervous system circuits that process thermal afferent inputs from the skin and the body core to control the activity of thermoeffectors. These include thermoregulatory behaviors, cutaneous vasomotion (vasoconstriction and, in humans, active vasodilation), thermogenesis (shivering and brown adipose tissue), evaporative heat loss (salivary spreading in rodents, and human sweating). This review provides an overview of the central nervous system circuits for thermoregulatory reflex regulation of thermoeffectors.
Topics: Animals; Body Temperature; Body Temperature Regulation; Humans; Neural Pathways; Shivering; Skin Temperature; Thermogenesis
PubMed: 30586638
DOI: 10.1016/j.neulet.2018.11.027 -
Annals of the Academy of Medicine,... Apr 2008This review discusses human thermoregulation during exercise and the measurement of body temperature in clinical and exercise settings. The thermoregulatory mechanisms... (Review)
Review
This review discusses human thermoregulation during exercise and the measurement of body temperature in clinical and exercise settings. The thermoregulatory mechanisms play important roles in maintaining physiological homeostasis during rest and physical exercise. Physical exertion poses a challenge to thermoregulation by causing a substantial increase in metabolic heat production. However, within a non-thermolytic range, the thermoregulatory mechanisms are capable of adapting to sustain physiological functions under these conditions. The central nervous system may also rely on hyperthermia to protect the body from "overheating." Hyperthermia may serve as a self-limiting signal that triggers central inhibition of exercise performance when a temperature threshold is achieved. Exposure to sub-lethal heat stress may also confer tolerance against higher doses of heat stress by inducing the production of heat shock proteins, which protect cells against the thermolytic effects of heat. Advances in body temperature measurement also contribute to research in thermoregulation. Current evidence supports the use of oral temperature measurement in the clinical setting, although it may not be as convenient as tympanic temperature measurement using the infrared temperature scanner. Rectal and oesophagus temperatures are widely accepted surrogate measurements of core temperature (Tc), but they cause discomfort and are less likely to be accepted by users. Gastrointestinal temperature measurement using the ingestible temperature sensor provides an acceptable level of accuracy as a surrogate measure of Tc without causing discomfort to the user. This form of Tc measurement also allows Tc to be measured continuously in the field and has gained wider acceptance in the last decade.
Topics: Body Temperature; Body Temperature Regulation; Exercise; Humans; Monitoring, Physiologic
PubMed: 18461221
DOI: No ID Found -
Physiology (Bethesda, Md.) Mar 2022Hypothermia is defined as a core body temperature of <35°C, and as body temperature is reduced the impact on physiological processes can be beneficial or detrimental.... (Review)
Review
Hypothermia is defined as a core body temperature of <35°C, and as body temperature is reduced the impact on physiological processes can be beneficial or detrimental. The beneficial effect of hypothermia enables circulation of cooled experimental animals to be interrupted for 1-2 h without creating harmful effects, while tolerance of circulation arrest in normothermia is between 4 and 5 min. This striking difference has attracted so many investigators, experimental as well as clinical, to this field, and this discovery was fundamental for introducing therapeutic hypothermia in modern clinical medicine in the 1950s. Together with the introduction of cardiopulmonary bypass, therapeutic hypothermia has been the cornerstone in the development of modern cardiac surgery. Therapeutic hypothermia also has an undisputed role as a protective agent in organ transplantation and as a therapeutic adjuvant for cerebral protection in neonatal encephalopathy. However, the introduction of therapeutic hypothermia for organ protection during neurosurgical procedures or as a scavenger after brain and spinal trauma has been less successful. In general, the best neuroprotection seems to be obtained by avoiding hyperthermia in injured patients. Accidental hypothermia occurs when endogenous temperature control mechanisms are incapable of maintaining core body temperature within physiologic limits and core temperature becomes dependent on ambient temperature. During hypothermia spontaneous circulation is considerably reduced and with deep and/or prolonged cooling, circulatory failure may occur, which may limit safe survival of the cooled patient. Challenges that limit safe rewarming of accidental hypothermia patients include cardiac arrhythmias, uncontrolled bleeding, and "rewarming shock."
Topics: Animals; Body Temperature; Heart Arrest; Humans; Hypothermia; Hypothermia, Induced; Rewarming
PubMed: 34632808
DOI: 10.1152/physiol.00025.2021 -
Autonomic Neuroscience : Basic &... Apr 2016Thermoregulation is a vital function of the autonomic nervous system in response to cold and heat stress. Thermoregulatory physiology sustains health by keeping body... (Review)
Review
Thermoregulation is a vital function of the autonomic nervous system in response to cold and heat stress. Thermoregulatory physiology sustains health by keeping body core temperature within a degree or two of 37°C, which enables normal cellular function. Heat production and dissipation are dependent on a coordinated set of autonomic responses. The clinical detection of thermoregulatory impairment provides important diagnostic and localizing information in the evaluation of disorders that impair thermoregulatory pathways, including autonomic neuropathies and ganglionopathies. Failure of neural thermoregulatory mechanisms or exposure to extreme or sustained temperatures that overwhelm the body's thermoregulatory capacity can also result in potentially life-threatening departures from normothermia. Hypothermia, defined as a core temperature of <35.0°C, may present with shivering, respiratory depression, cardiac dysrhythmias, impaired mental function, mydriasis, hypotension, and muscle dysfunction, which can progress to cardiac arrest or coma. Management includes warming measures, hydration, and cardiovascular support. Deaths from hypothermia are twice as frequent as deaths from hyperthermia. Hyperthermia, defined as a core temperature of >40.5°C, may present with sweating, flushing, tachycardia, fatigue, lightheadedness, headache, and paresthesia, progressing to weakness, muscle cramps, oliguria, nausea, agitation, hypotension, syncope, confusion, delirium, seizures, and coma. Mental status changes and core temperature distinguish potentially fatal heat stroke from heat exhaustion. Management requires the immediate reduction of core temperature. Ice water immersion has been shown to be superior to alternative cooling measures. Avoidance of thermal risk and early recognition of cold or heat stress are the cornerstones of preventive therapy.
Topics: Animals; Body Temperature; Body Temperature Regulation; Cold Temperature; Fever; Hot Temperature; Humans; Hypothermia
PubMed: 26794588
DOI: 10.1016/j.autneu.2016.01.001 -
Journal of Applied Physiology... Nov 2019During the past several decades, the incidence of exertional heat stroke (EHS) has increased dramatically. Despite an improved understanding of this syndrome, numerous... (Review)
Review
During the past several decades, the incidence of exertional heat stroke (EHS) has increased dramatically. Despite an improved understanding of this syndrome, numerous controversies still exist within the scientific and health professions regarding diagnosis, pathophysiology, risk factors, treatment, and return to physical activity. This review examines the following eight controversies: ) reliance on core temperature for diagnosing and assessing severity of EHS; ) hypothalamic damage induces heat stroke and this mediates "thermoregulatory failure" during the immediate recovery period; ) EHS is a predictable condition primarily resulting from overwhelming heat stress; ) heat-induced endotoxemia mediates systemic inflammatory response syndrome in all EHS cases; ) nonsteroidal anti-inflammatory drugs for EHS prevention; ) EHS shares similar mechanisms with malignant hyperthermia; ) cooling to a specific body core temperature during treatment for EHS; and ) return to physical activity based on physiological responses to a single-exercise heat tolerance test. In this review, we present and discuss the origins and the evidence for each controversy and propose next steps to resolve the misconception.
Topics: Anti-Inflammatory Agents, Non-Steroidal; Body Temperature; Body Temperature Regulation; Cryotherapy; Exercise; Heat Stroke; Humans; Physical Exertion; Risk Factors
PubMed: 31545156
DOI: 10.1152/japplphysiol.00452.2019 -
Neuron Feb 2023Precise monitoring of internal temperature is vital for thermal homeostasis in mammals. For decades, warm-sensitive neurons (WSNs) within the preoptic area (POA) were...
Precise monitoring of internal temperature is vital for thermal homeostasis in mammals. For decades, warm-sensitive neurons (WSNs) within the preoptic area (POA) were thought to sense internal warmth, using this information as feedback to regulate body temperature (T). However, the cellular and molecular mechanisms by which WSNs measure temperature remain largely undefined. Via a pilot genetic screen, we found that silencing the TRPC4 channel in mice substantially attenuated hypothermia induced by light-mediated heating of the POA. Loss-of-function studies of TRPC4 confirmed its role in warm sensing in GABAergic WSNs, causing additional defects in basal temperature setting, warm defense, and fever responses. Furthermore, TRPC4 antagonists and agonists bidirectionally regulated T. Thus, our data indicate that TRPC4 is essential for sensing internal warmth and that TRPC4-expressing GABAergic WSNs function as a novel cellular sensor for preventing T from exceeding set-point temperatures. TRPC4 may represent a potential therapeutic target for managing T.
Topics: Mice; Animals; Body Temperature; Body Temperature Regulation; Hypothalamus; Preoptic Area; GABAergic Neurons; Mammals
PubMed: 36476978
DOI: 10.1016/j.neuron.2022.11.008