Department of Physiology, Faculty of Medicine, Masaryk University1
Thermoregulation
Physiology II lecture (aZLFY0422p)
Tibor Stračina
Physiology II lecture (aZLFY0422p)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 (aZLFY0422p)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
Physiology II lecture (aZLFY0422p)4
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 (aZLFY0422p)5
Variations of body core temperature
̶ Circadian rhythm
̶ Circamensal rhythm (women
between puberty and menopause)
̶ Seasonal variations (circannul
rhythm)
̶ Ageing
Physiology II lecture (aZLFY0422p)6
Variations of body core temperature
Physiology II lecture (aZLFY0422p)7
A fine balance of body core temperature
HEAT
PRODUCTION
HEAT
INTAKE
HEAT
OUTPUT
HEAT
LOSS
Physiology II lecture (aZLFY0422p)8
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 (aZLFY0422p)9
Transfer of heat within the body
̶ primarily by CONVECTION
̶ medium = blood
̶ minor amount by CONDUCTION
̶ direct contact of organs/tissues
Physiology II lecture (aZLFY0422p)10
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)
Physiology II lecture (aZLFY0422p)11
Heat intake and loss
̶ passive processes
̶ RADIATION
̶ CONVECTION
̶ CONDUCTION
̶ skin-environment temperature gradient
Physiology II lecture (aZLFY0422p)12
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)
Physiology II lecture (aZLFY0422p)13
Thermoregulation
̶ All processes involved in keeping the body core temperature within the range
̶ Thermoregulatory behaviour
̶ Social thermoregulation
Physiology II lecture (aZLFY0422p)14
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
Physiology II lecture (aZLFY0422p)15
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 (aZLFY0422p)16
Thermal effectors
̶ Behaviour
̶ Cutaneous circulation
̶ Sweat glands
̶ Skeletal muscles (shivering)
̶ Horripilation
̶ Brown adipose tissue (nonshivering thermogenesis)
Physiology II lecture (aZLFY0422p)17
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 (aZLFY0422p)18
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
Department of Physiology, Faculty of Medicine, Masaryk University19
Physiology of Exercise
Physiology II lecture (aZLFY0422p)
Tibor Stračina
Physiology II lecture (aZLFY0422p)20
Work (physical activity, exercise)
Source: www.freepik.com. Photos created by freepik and standret
Physiology II lecture (aZLFY0422p)21
Skeletal muscle
̶ Contraction: isometric (static work) vs. isotonic (dynamic work)
̶ Blood flow depends on muscle tension
̶ Metabolic autoregulation: ↓pO2; ↑pCO2; ↓pH; ↑K+; ↑local temperature
̶ Metabolism: aerobic vs. anaerobic
̶ Muscle spindles – muscle tension – afferentation of exercise pressor reflex
Physiology II lecture (aZLFY0422p)22
Skeletal muscle metabolism
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aZLFY0422p)23
Reaction of the body to exercise
̶ Sympathetic NS (ergotropic system)
̶ Cardiovascular changes
̶ Respiratory changes
̶ Metabolic changes
̶ HOMEOSTASIS
Physiology II lecture (aZLFY0422p)24
Anticipation of exercise
̶ Reaction of the body (cardiovascular system)
̶ Prepare the body for the increased metabolism of the exercising skeletal
muscles
̶ Same as the early response to exercise
̶ Resembling fight-or-flight reaction
Physiology II lecture (aZLFY0422p)25
Cardiovascular response to exercise
̶ Increased cardiac output
̶ Vasoconstriction in inactive skeletal muscles, the GIT, skin, (kidneys)
̶ Vasodilation in active muscles (metabolic autoregulation)
̶ Increased venous return
̶ Histamine release
̶ Epinephrine release (adrenal medulla)
̶ Thermoregulation
Physiology II lecture (aZLFY0422p)26
Increase of cardiac output. Cardiac reserve
̶ CO = SV x HR (SNS: positive inotropic and chronotropic effect)
̶ Cardiac reserve = maximal CO / resting CO (4 – 7)
̶ Coronary reserve = maximal CF / resting CF (~3.5)
̶ Chronotropic reserve = maximal HR / resting HR (3 – 5)
̶ Volume reserve = maximal SV / resting SV (~1.5)
CO – cardiac output; CF – coronary flow; HR – heart rate; SV – stroke volume
Physiology II lecture (aZLFY0422p)27
Changes of arterial blood pressure
PARAMETER AT REST DURING EXERCISE INCREASE (x)
Cardiac output
[L/min]
5 – 6 25 (35) 4 – 5 (7)
cardiac reserve
Heart rate
[1/min]
(45) 60-90 190 – 200 (220)
age-dependent
3 – 5
chronotropic reserve
Stroke volume
[mL]
75 115 ~1.5
volume reserve
Systolic BP
[mmHg]
120 static work ↑
dynamic work ↑↑
Diastolic BP
[mmHg]
70 static work ↑↑↑
dynamic work ─ / ↓
Mean arterial P (MAP)
[mmHg]
~90 static work ↑
dynamic work ─ / ↑
Muscle persufion
[mL/min/100g]
2 – 4 60 – 120 (180)
static vs. dynamic work
30
(10% COmax)
Physiology II lecture (aZLFY0422p)28
Respiratory response to exercise
̶ Respiratory centre - ↑ ventilation
̶ chemoreceptors: ↑ pCO2 + ↓ pH
̶ proprioceptors in lungs
̶ Sympathetic stimulation (stress – anticipation)
Physiology II lecture (aZLFY0422p)29
Respiratory response to exercise
PARAMETER AT REST DURING EXERCISE INCREASE (x)
Ventilation
[L/min]
6 – 12 90 – 120 15 – 20
respiratory reserve
Breathing frequency
[1/min]
12 – 16 40 – 60 4 – 5
Tidal volume (VT)
[mL]
0.5 – 0.75 ~2 3 – 4
Pulmonary artery blood flow
[mL/min]
5 – 6 25 – 35 4 – 6
O2 uptake (VO2)
[mL/min)]
250 – 300 ~3000 10 – 12 (25)
CO2 production
[mL/min]
~200 ~8000 ~40
Physiology II lecture (aZLFY0422p)30
Oxygen uptake by lungs
̶ Spiroergometry
̶ Resting VO2: ~3.6 mL O2 / (min x kg)
̶ VO2 max – objective index for aerobic power
̶ untrained middle age person: 30 – 40 mL O2 / (min x kg)
̶ elite endurance athletes: 80 – 90 mL O2 / (min x kg)
̶ HF / COPD patients: 10 – 20 mL O2 / (min x kg)
Adopted from:
https://studentconsult.inkling.com/read/boron-
medical-physiology-3e/chapter-60/figure-60-6
Physiology II lecture (aZLFY0422p)31
Determinants of VO2 max
1. Uptake of O2 by the lungs
̶ pulmonary ventilation
2. O2 delivery to the muscles
̶ blood flow (pressure gradient – cardiac output x resistence)
̶ haemoglobin concentration
3. Extraction of O2 from blood by muscle
̶ pO2 gradient: blood-mitochondria
Physiology II lecture (aZLFY0422p)32
Oxygen consumption during exercise
̶ Oxygen debt
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aZLFY0422p)33
Blood gases during exercise
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aVLFY0422p)34
Energy substrate used by skeletal muscle
during exercise
̶ Low-intensity e.: fats
̶ High-intensity e.: glucose
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aZLFY0422p)35
Energy substrate use – aerobic vs. anaerobic
Adopted from: D.U.Silverthorn:
Human Physiology (An Integrated
Approach)
Physiology II lecture (aZLFY0422p)36
Testing of fitness
̶ Spiroergometry
̶ Standardised workload
̶ accurate: in W/kg
̶ comparative (simple, inaccurate): in MET
̶ metabolic equivalent (actual MR / resting MR)
̶ 1 MET = uptake of 3.5 ml O2/kg.min ≈ 4.31 kJ/kg.h
̶ sleeping ≈ 0.9 MET; slow walking ≈ 3-4 MET; fast running ≈ 16 MET
Physiology II lecture (aZLFY0422p)37
Indexes of fitness
̶ W170 [W/kg]
̶ VO2 max [mL O2 / (min x kg)]
̶ Aerobic / anaerobic threshold
̶ Fatigue
̶ Training
̶ Adaptation to exercise
Department of Physiology, Faculty of Medicine, Masaryk University38
Adaptation
Physiology II lecture (aZLFY0422p)
Tibor Stračina
Physiology II seminar (aZLFY0422s)39
Adaptation
̶ Long-term functional and/or structural change as a response to
long-term or repeated change (on certain level) of the environment
̶ Leads to decrease of energetic demand for keeping homeostasis
in changed conditions
̶ Evolution (fixed adaptation)
Physiology II seminar (aZLFY0422s)40
Adaptation to exercise:
Strength vs. Endurance training
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Physiology II seminar (aZLFY0422s)41
Adaptation to exercise
̶ Skeletal muscles
̶ Hypertrophy, vascularization
̶ Cardiovascular system
̶ Heart adaptation (concentric hypertrophy vs. athletic heart)
̶ Increase in RBC and heamoglobin concentration
̶ Respiratory system
̶ Increase in VC (if possible), increase in maximal respiartion (increase in respiratory reserve), more effective
diffusion on alveolo-capillar membrane
̶ Metabolism
Physiology II seminar (aZLFY0422s)42
Athletic heart
̶ Adaptation to endurance training
̶ ↑ LVEDV - ↑ SV - (baroreflex) ↓ HR
̶ ~ CO
̶ ↑ chronotropic reserve = ↑ cardiac
reserve
Source: https://assets.beta.meta.org/discover/thematic-feed/83-athletic-heart-syndrome.jpg
Physiology II lecture (aZLFY0422p)43
Cardiac reserve in trained and untrained
0
10
20
30
40
0 1 2 3 4 5
CO[L/min]
External power output [W/kg]
trained (athletic heart)
untrained
(physiological response)
heart failure
Physiology II lecture (aZLFY0422p)44
Oxygen uptake in trained and untrained
Source:
https://studentconsult.inkling.com/r
ead/boron-medical-physiology-
3e/chapter-60/figure-60-6
Physiology II seminar (aZLFY0422s)45
Adaptation to extreme temperatures
Source: www.freepik.com
Physiology II lecture (aVLFY0422p)46
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.