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Thermal Physiology and Thermoregulation
Published in James Stewart Campbell, M. Nathaniel Mead, Human Medical Thermography, 2023
James Stewart Campbell, M. Nathaniel Mead
The hypothalamus integrates inputs from thermoreceptors in both the skin and core organs. Activation of warm thermoreceptors may cause inhibition of cold receptors.16 Specialized neuronal thermoreceptors in the hypothalamus constantly compare arterial blood temperature to an internal set point. This temperature setting may vary with individuals and with circadian rhythms; core temperature typically fluctuates between average values of 36.4°C (97.5°F) in the morning and 36.9°C (98.4°F) in the evening.17 Various pathological processes can induce either systemic or local thermal anomalies; for example, core temperature may increase due to infection, inflammation, trauma, and malignancy, while limb temperature may decrease due to ischemia or increase due to inflammation.
Inflammation
Published in George Feuer, Felix A. de la Iglesia, Molecular Biochemistry of Human Disease, 2020
George Feuer, Felix A. de la Iglesia
The maintenance of normal body temperature is controlled by a complex set of reactions and feedback mechanisms associated with the production and dissipation of body heat. These reactions are triggered by the hypothalamus as a response to stimuli received from thermoreceptors. These receptors are present abundantly in the skin and possibly in the hypothalamus itself, in the spinal cord, and in the viscera. An interaction between the peripheral and central mechanisms determines the response of the body to internal or external environmental temperature changes. The temperature of the blood flowing through the hypothalamus appears to be the most important factor in the initiation of heat changes. The thermostatic set point of this organ in man reacts very sensitively to changes as small as a fraction of 1°. When the temperature of the blood perfusing the hypothalamus is raised, there is loss of heat via vasodilation, perspiration, and panting. During fever, hypothalamic temperature regulation is still obtained, but at a higher baseline level.
Basic Thermal Physiology: What Processes Lead to the Temperature Distribution on the Skin Surface
Published in Kurt Ammer, Francis Ring, The Thermal Human Body, 2019
The “Glossary of Terms for Thermal Physiology” defines a thermoreceptor (synonym: temperature receptor) as thermosensitive neural element for which both its afferent function and its response characteristics are electro-physiologically identified. Thermoreceptors have been unequivocally identified, so far, only in the skin and mucous surfaces as cold receptors, warm receptors, and infrared receptors in some snake species, vampire bats and insects including forest fire-seeking beetles, certain butterflies and bloodsucking bugs [5].
Human cold habituation: Physiology, timeline, and modifiers
Published in Temperature, 2022
Beau R. Yurkevicius, Billie K. Alba, Afton D. Seeley, John W. Castellani
Small mammals also demonstrate physiological adaptations to prolonged cold exposure [22]. When rats are housed in a 5°C environment for 6 weeks, the sensitivity of central and peripheral thermoreceptors that are responsive to low temperatures decreases while the sensitivity of those receptors responsive to warm temperatures increases [22]. These findings are consistent with observations that organisms allow for a greater reduction in core temperature before activating cold defense responses. In cold-adapted cats (5 vs 30°C ambient air), the average dynamic peak frequency of nasal cold fibers during a 5°C cooling perturbation is significantly reduced compared to non-adapted cats [23]; however, this change in thermoreceptor activity has only been observed following long term (~4.5 yrs) cold exposure and not short-term (2 mos.) cold exposure [24,25]. Nonetheless, these studies raise the question as to whether reduced sensory input or thermoreceptor sensitivity contribute to the blunted thermoeffector responses in humans.
Influences of ovarian hormones on physiological responses to cold in women
Published in Temperature, 2022
Andrew M. Greenfield, Nisha Charkoudian, Billie K. Alba
In response to body cooling, afferent signals from peripheral and central thermoreceptors are sensed by the pre-optic region of the anterior hypothalamus (PO/AH), from which efferent signals elicit insulative (i.e., cutaneous vasoconstriction) and metabolic (e.g., shivering and nonshivering thermogenesis) thermoregulatory effector responses. The early and sustained response to cold exposure is characterized by constriction of cutaneous blood vessels and a subsequent reduction in skin blood flow [17,18]. The vasoconstrictor response to skin cooling reduces the skin-to-air temperature gradient and thus minimizes convective heat loss during cold exposure. As cooling continues and cutaneous vasoconstriction becomes insufficient to prevent decreases in core temperature, metabolic heat production increases to offset heat loss [19,20].
Individualized analysis of skin thermosensory thresholds and sensitivity in heat-sensitive people with multiple sclerosis
Published in Temperature, 2021
Davide Filingeri, Georgia Chaseling, Aikaterini Christogianni, Kaltrina Feka, Antonino Bianco, Scott L Davis, Ollie Jay
Afferent inputs from warm- and cold-sensitive thermoreceptors innervating the skin contribute to the conscious perception of temperature stimuli, i.e. thermal sensations [9], and provide the perceptual drive to trigger thermoregulatory behaviors [10]. Two objective measures define the performance of the afferent thermosensory pathway sub-serving thermal sensations, i.e. the threshold (i.e. smallest amount of temperature change that can be perceived on the skin) and sensitivity (i.e. the ability to discriminate the magnitude of progressively greater temperature stimuli) to thermal stimuli [9]. Assessing whether MS induces deficiencies in threshold for and sensitivity of thermal sensations provides an opportunity to characterize impairments in perceptual thermosensory pathways in heat-sensitive MS patients, which can be relevant to better understand the impact of MS-induced sensory deficits on thermoregulatory behaviors important for heat resilience (e.g. reducing clothing insulation when skin temperature increases).