Temperature Regulation
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
Under general anaesthesia in a cold operating room environment, the interthreshold range is widened from 0.4°C to 4°C (between 36.7°C and 37.1°C) and the behavioural responses are completely abolished. Within this expanded interthreshold range, the patients are poikilothermic as active thermoregulatory responses are absent so that body temperature changes passively in proportion to the difference between metabolic heat production and heat lost to the environment. The only thermoregulatory responses available to anaesthetized, paralysed and hypothermic patients are vasoconstriction and non-shivering thermogenesis. Non-shivering thermogenesis appears to increase metabolic heat production significantly in hypothermic infants. The effect of these physiological disturbances is an inability of the body to respond effectively to the multiple factors that cause intraoperative hypothermia.
The Influence of Hormones on Infectious and Parasitic Disease
Istvan Berczi in Pituitary Function and Immunity, 2019
Fever has been recognized as a sign of infectious disease from at least the time of Hippocrates. The recognition of the potential significance of fever, however, did not occur until recently. The first indication for the biological significance of fever was the observation of Kluger et al.15 that lizards seek warmer environments to raise their body temperature to febrile levels when infected. This behavioral modification of body temperature has survival value. Other poikilotherms, including fish, behave similarly. In mammals, fever is induced by an endogenous pyrogenic substance produced by monocyte/macrophage-type cells. This pyrogen appears to be identical with interleukin 1, which is a lymphocyte activating factor, playing a fundamental role in the initiation of most, if not all, immune reactions.16,17 Several in vitro functions of mammalian lymphoid cells, such as lectin induced mitogenesis of thymocytes, lymphokine production, interleukin 1 induced T cell proliferation, and antibody production are elevated significantly at febrile temperature (39°C).18–20
Metabolism, nutrition, exercise and temperature regulation
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
General anaesthesia increases the interthreshold range by decreasing the thermoregulatory threshold to cold by approximately 2.5°C and increasing the threshold temperature by approximately 1.3°C. Within this expanded interthreshold range, the patients are poikilothermic as active thermo-regulatory responses are absent so that body temperature changes passively in proportion to the difference between metabolic heat production and heat lost to the environment. The only thermo-regulatory responses available to anaesthetized, paralysed and hypothermic patients are vasoconstriction and non-shivering thermogenesis. The core temperature at which thermoregulatory threshold triggers peripheral vasoconstriction is agent and dose dependent. Non-shivering thermogenesis appears to increase metabolic heat production significantly in hypothermic infants.
Human thermal perception and time of day: A review
Published in Temperature, 2021
Marika Vellei, Giorgia Chinazzo, Kirsi-Marja Zitting, Jeffrey Hubbard
Humans, like nearly all mammals and avian species, are homeotherms (warm-blooded), meaning that their internal body temperature remains stable irrespective of environmental influence [26]. This is in contrast to poikilotherms (cold-blooded), such as fish, reptiles, and amphibians, whose internal temperature fluctuates widely depending on different factors, and can both influence metabolic rate and radically alter cellular processes (i.e. protein denaturing at high temperature) [27]. In the past, thermoregulation was thought to be exclusively under the control of the preoptic hypothalamus, a brain region located posterior to the optic nerve, and ventral to cortical structures [28]. Generally speaking, the hypothalamus is responsible for the regulation of a wide array of autonomic functions, including appetite and sleep initiation, and forms a critical part of the hypothalamic-pituitary-adrenal axis, which controls among others, stress reactions. In recent years, however, its role in regards to being the sole controller of thermoregulation in the brain has been redefined [29]. For example, thermoreceptors have been found in other areas, including the brain stem, and indeed in other central nervous system structures such as the spinal cord [30], underscoring the fact that the thermoregulatory system is diffuse [31].
The sine qua non of the fish invitrome today and tomorrow in environmental radiobiology
Published in International Journal of Radiation Biology, 2022
Fish are considered to be the most radiosensitive animal group for aquatic poikilotherms (Sazykina and Kryshev 2003). As of today, 35,423 fish species have been identified, accounting for 49% of all vertebrates (IUCN 2020). It is perhaps most fitting to study aquatic health using fish species because of their complete dependence on water for the entire or a vital part of their life. Fish also are an important component of the food web and radiological contamination can affect food safety for human consumption. As the biology and radiosensitivity of mammals and fish are vastly different (Whicker and Schultz 1982), using human/mammalian data to predict what could happen to fish is inappropriate. To date, radiobiological effects have been studied in only a small number of fish species, thus limiting how we understand various adaptive mechanisms fish species use to respond to stressors. It is a challenge to examine so many fish species in a well-planned-out and well-thought-out studies due to time, labor, funding and technical constraints. There is nevertheless a need to expand studies with more fish species in both acute and chronic exposure to different radiation types. Such a need seeks an approach that is more accessible while still generating important information.
Sexual dimorphism in ultradian and 24h rhythms in plasma levels of growth hormone in Indian walking catfish, Clarias batrachus
Published in Chronobiology International, 2021
Raj Naresh Gopal, Dhanananajay Kumar, Vinay Kumar Singh, Atanu Kumar Pati, Bechan Lal
Fish, being poikilotherm, are influenced by daily and seasonal variations in photoperiod, temperature, rainfall, physico-chemical, and biological characteristics of the aquatic ecosystem, such as dissolved O2, CO2, pH, and salinity. Biological rhythms are recurrent processes, from molecular to behavioral levels, controlled by endogenous oscillators or biological clocks. These rhythmic processes are the output of interactions between the biological clock and external environment (Lamont and Amir 2010) that provide adaptive fitness to organisms by appropriately timing their behavior (feeding, locomotion, and social aggregation) and physiology (growth, reproduction, immune response, and hormone secretion). In fish, rhythmic secretion of various metabolic and reproductive hormones, such as gonadotropin (De Vlaming and Vodicnik 1977; Harikrishnan et al. 2002; Hontela and Peter 1978; Khan and Thomas 1994), sex steroids (Lamba et al. 1983; Singh and Singh 1987), and thyroid hormones (Eales et al. 1981; Sinha et al. 1992; Stacey et al. 1984) has been reported. In vertebrates, rhythmic secretion of these hormones controls and coordinates growth and reproduction, two crucial physiological processes.
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