Department of Physiology, Faculty of Medicine, Masaryk University1
Thermoregulation
Physiology II lecture (aVLFY0422p)
Tibor Stračina
Physiology II lecture (aVLFY0422p)2
The presentation is copyrighted work created by employees of
Masaryk University. Any unauthorized reproduction or distribution
of the presentation or individual slides is against the law.
Physiology II lecture (aVLFY0422p)3
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
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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)
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Variations of body core temperature
̶ Circadian rhythm
̶ Circamensal rhythm (women
between puberty and menopause)
̶ Seasonal variations (circannul
rhythm)
̶ Ageing
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Variations of body core temperature
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A fine balance of body core temperature
HEAT
PRODUCTION
HEAT
INTAKE
HEAT
OUTPUT
HEAT
LOSS
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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)
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Transfer of heat within the body
̶ primarily by CONVECTION
̶ medium = blood
̶ minor amount by CONDUCTION
̶ direct contact of organs/tissues
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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)
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Heat intake and loss
̶ passive processes
̶ RADIATION
̶ CONVECTION
̶ CONDUCTION
̶ skin-environment temperature gradient
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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)
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Thermoregulation
̶ All processes involved in keeping the body core temperature within the range
̶ Thermoregulatory behaviour
̶ Social thermoregulation
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Afferentation
̶ Central thermoreceptors – deep brain temperature
̶ temperature-sensitive neurons in anterior preoptic hypothalamus
̶ Peripheral thermoreceptors – skin temperature
̶ TRP channels
Adopted from:: https://doi.org/10.1016/bs.pmbts.2015.01.002
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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)
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Thermal effectors
̶ Behaviour
̶ Cutaneous circulation
̶ Sweat glands
̶ Skeletal muscles (shivering)
̶ Horripilation
̶ Brown adipose tissue (nonshivering thermogenesis)
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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)
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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
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The presentation is copyrighted work created by employees of
Masaryk University. Any unauthorised reproduction or distribution
of the presentation or individual slides is against the law.