Department of Physiology, Faculty of Medicine, Masaryk University1 Thermoregulation Physiology II lecture (aVLFY0422p) Tibor Stračina Physiology II lecture (aVLFY0422p)2 Body temperature – homeostatic parameter 45 40 35 30 25 Heat stroke Hard exercise, fever Normal body temperature (36,3 – 37,1°C) Loss of consciousness Muscle failure, cardiac fibrillation HYPER- THERMIA HYPO- THERMIA Physiology II lecture (aVLFY0422p)3 Body core vs. shell ̶ homeotherms vs. poikilotherms ̶ Body core temperature – regulated within certain (narrow) range ̶ Skin temperature (shell) – more variable (ambient t., core body t.) Adopted from: K.S. Saladin, Anatomy & Physiology—The Unity of Form and Function, 8th ed. (McGraw-Hill, 2018) Physiology II lecture (aVLFY0422p)4 Variations of body core temperature ̶ Circadian rhythm ̶ Circamensal rhythm (women between puberty and menopause) ̶ Seasonal variations (circannul rhythm) ̶ Ageing Physiology II lecture (aVLFY0422p)5 Variations of body core temperature Physiology II lecture (aVLFY0422p)6 Heat vs. temperature ̶ Heat [J] – energy transfered to or from the system; measure of the internal energy state ̶ Temperature [K, °C, °F] – a measure of heat content; mean kinetic energy of the particles (molecules, ions) Physiology II lecture (aVLFY0422p)7 A fine balance of body core temperature HEAT PRODUCTION HEAT INTAKE HEAT OUTPUT HEAT LOSS Physiology II lecture (aVLFY0422p)8 Heat production ̶ Metabolism: metabolic rate ≈ heat production ̶ Physical activity (active muscle contraction) – rest vs. exercise ̶ Postprandial thermogenesis (food intake) ̶ Shivering thermogenesis ̶ Non-shivering thermogenesis (brown adipose tissue) HEAT PRODUCTION HEAT INTAKE HEAT OUTPUT HEAT LOSS Physiology II lecture (aVLFY0422p)9 Transfer of heat within the body ̶ primarily by CONVECTION ̶ medium = blood ̶ minor amount by CONDUCTION ̶ direct contact of organs/tissues Physiology II lecture (aVLFY0422p)10 Heat intake and loss ̶ passive processes ̶ RADIATION ̶ CONVECTION ̶ CONDUCTION ̶ skin-environment temperature gradient HEAT PRODUCTION HEAT INTAKE HEAT OUTPUT HEAT LOSS Physiology II lecture (aVLFY0422p)11 Heat output (active loss) ̶ EVAPORATION ̶ sensible perspiration = sweat production (1 L of evaporated s. = 2 428 kJ) ̶ insensible perspiration = diffusion of water through skin and mucosae ̶ from the skin to the environment ̶ (RADIATION) ̶ (CONDUCTION) ̶ (CONVECTION) HEAT PRODUCTION HEAT INTAKE HEAT OUTPUT HEAT LOSS Physiology II lecture (aVLFY0422p)12 Thermoregulation ̶ All processes involved in keeping the body core temperature within the range ̶ Thermoregulatory behaviour ̶ Social thermoregulation Physiology II lecture (aVLFY0422p)13 Peripheral Thermoreceptors Central Thermoreceptors HYPOTHALAMUS (POA) Thermoregulatory Centre Skin Arterioles Skeletal Muscle Sweat Glands Skin Temperature Deep Brain Temperature BodyCoreTemperature Pilo- erection BAT Endocrine response Ambient Temperature Behaviour Physiology II lecture (aVLFY0422p)14 Afferentation - thermoreceptor ̶ Central thermoreceptors – deep brain temperature ̶ temperature-sensitive neurons in anterior preoptic hypothalamus ̶ Peripheral thermoreceptors ̶ Skin thermoreceptor - skin temperature ̶ Thermoreceptors in GIT ̶ Thermoreceptors in liver and other organs ̶ Thermoreceptors in skeletal muscles Adopted from:: https://doi.org/10.1016/bs.pmbts.2015.01.002 Physiology II lecture (aVLFY0422p)15 Principle of thermorecetion: TRP channels ̶ Protein superfamily ̶ Mixed cation channels ̶ Activation leads to membrane depolarization ̶ Polymodal ̶ Thermosensitive Adopted from:: https://doi.org/10.1016/bs.pmbts.2015.01.002 Physiology II lecture (aVLFY0422p)16 Thermoregulatory centre ̶ anterior preoptic HYPOTHALAMUS ̶ integration of afferent information ̶ modifying the efferent pathways (vegetative, somatic) to the thermal effectors ̶ „set-point“ vs. threshold temperature for the effector(s) Physiology II lecture (aVLFY0422p)17 Thermal effectors ̶ Behaviour ̶ Cutaneous circulation ̶ Sweat glands ̶ Skeletal muscles (voluntary movements, shivering) ̶ Horripilation ̶ Brown adipose tissue (nonshivering thermogenesis) ̶ Role of sympathetic nervous system (see VLFY0422s demonstration) Physiology II lecture (aVLFY0422p)18 Endocrine reaction in thermoregulation ̶ Epinephrin and norepinephrin ̶ Thermogenic effect ̶ A part of sympathoadrenal reaction in „cold stress“ (extreme and/or prolonged exposure to cold) ̶ Thyroid hormones (T3 and T4) ̶ Thermogenic effect – increase in BMR ̶ Subacute / chronic effect ̶ Long-term hyper-/hypo-production is involved in adaptation to cold / warm environment ̶ Indirect relationship with ADH and aldosterone Physiology II lecture (aVLFY0422p)19 Cold-induced thermoregulatory mechanisms ̶ Decrease of heat loss ̶ Behaviour: Decrease of body surface, taking warm clothes ̶ Vasoconstriction in the skin. Horripilation ̶ Inhibition of sweating ̶ Increase of heat production ̶ Skeletal muscles: Intentional movements (behaviour). Shivering ̶ Nonshivering thermogenesis (brown adipose tissue, NA, β3R, UCP1) ̶ Hunger (increas of food intake) Physiology II lecture (aVLFY0422p)20 Warm-induced thermoregulatory mechanisms ̶ Increase of heat loss/output ̶ Skin vasodilatation ̶ Increase of sweating (evaporation) ̶ Increase of ventilation ̶ Decrease of heat production/intake ̶ Behaviour: Moving out of the sun, taking light clothes. Inactiveness (decrease of intentional movements), apathy ̶ Loss of appetite Physiology II lecture (aVLFY0422p)21 Thermoregulation in high humidity ̶ High humidity decreses rate of evaporation ̶ Sweating becomes uneffective and leads to water loss ̶ To dry the skin regularly can increase the effectivity of evaporation (clothing, wiping with towel) ̶ High risk of overheating and dehydration ̶ The risk is increased by physical activity! ̶ T 35°C and RH >60% is not safe for any phys. activity in non-adapted person Physiology II lecture (aVLFY0422p)22 Thermoregulation in physical activity ̶ Physical activity = increase in heat production ̶ Physical activity = decrease in the effective volume of circulating fluids ̶ Shift of the fluid to interstitial space ̶ Loss of fluids by sweating ̶ Maintaining the effective volume of circulating fluids (blood pressure) is always preferred over increasing active heat loss (thermoregulation) ̶ Body core temperature increases ̶ Ambient temperature play a crucial role ̶ Role of sympathetic nervous system (see VLFY0422s demonstration) Physiology II lecture (aVLFY0422p)23 Thermoregulation in children ̶ Shifted ration between body surface and overal body mass ̶ Newborns and children <3 years – uneffective central thermoregulatory mechanisms ̶ Higher risk of hyper- and hypo-thermia ̶ Higher risk of dehydration in heat stress Physiology II lecture (aVLFY0422p)24 Thermoregulation in old people ̶ Decreased skin sensitivity to cold and warm ̶ Reduced ability to actively release heat ̶ Decreasein number and activity of sweat glands ̶ Reduced cardiac reserve ̶ Reduced ability to produce heat ̶ Decrease in metabolic rate ̶ Reduced muscle mass (sarcopaenia) ̶ In old age, reduced ability to thermoregulate leads to greater fluctuations in core temperature Physiology II lecture (aVLFY0422p)25 Thermoregulation and body art ̶ Body art (tattoos, scarification, subdermal implants) can damage the sweat glands ̶ If body art covers large areas of skin, it can reduce the body's ability to cool itself ̶ The organism can thus be at risk of overheating, especially with greater heat stress (exposure to heat, physical activity) ̶ For elite athletes, body art on large areas of skin can limit performance Physiology II lecture (aVLFY0422p)26 The presentation is copyrighted work created by employees of Masaryk University. 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