MUNI
MED
THERMOREGULATION
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
Heat vs. temperature
- Heat [J] - (heat) energy transmitted/shared among the objects (passed or received)
- Temperature [K, °C5 °F] - degree of heat energy content; mean kinetic energy of particles (molecules, ions)
2    Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Endothermic („warm-blooded") vs. ectothermic („cold-blooded") species Arctic (20° - 40°C) vs. tropic (22° - 27°C water, 32° - 35°C) animals
MUNI
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University MED
Temperature - homeostatic parameter
Temperature (C) Symptoms	
28	muscle failure
30	loss of body temperature control
33	loss of consciousness
37	normal
42	central nervous system breakdown
44	death
Sunstroke
Intensive physical exercise, fever
Normal body temperature (36.3- 37.1°C)
Loss of consciousness
Skeletal muscles failure, ventricular fibrillation
4    Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
Core vs. Periphery (Shell)
homeothermic vs. Poikilothermie
Core temperature - kept within (narrow) range
Skin temperature (periphery, shell) -changing (depends on core and ambient temperatures)
5    Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University        Adopted from: K.S. Saladin, Anatomy & Physiology—The
Unity of Form and Function, 8th ed. (McGraw-Hill, 2018)
Variability of core temperature
Circadian rhythm
■c
37.4 O   37.2 -f 370
L
Š
° 366
36.4
-	
V	/
. 99.4
99.0
93 2
9        12 15
Time of Day
la
21
Circamensal rhythm (women from puberty to menopause)
3	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3		3	3	3		3	3	3	3	3
2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2	2			Y2				;			2	2	2
1	1	1	1	1	1	1	1	1	1	t	1	1	1	t	1		:		1	1	1	1	i	1	1		i	1
98	56	56	98	5<i	98	98	98	98	98	98	98	98	98	98		98	56		93	96	96	98	98	:«	Í6	9E		
9	9	9	9	9	9	9	9	9	9	9	9	9	9	9		9	9	9	9	9	9	9	9	9	9	9		9
S	8	8	8	8	8	8	8	8		8	8	8	8		8	8	8	8	8	8	8	8	8	8	8	8	-	:
	■				■								■				■		■		'				■		■	7
	•	•	■	■	■	■	■	■	M	■	■	■	•		■	■	-	■	•	■	■	■	•	■	■	■	-	<
■'			5	5	5	5	5	Si	5		5	5	5	ft	5	5	5	5	5	5	5	5	5	5	5	5	5	
4	4	4		4	4	4	4		4		4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	4	í
3	3	3	3		3		3		3		, j		3 J	3	3	3	3	3	3	3	3	3	3	3	3	3	3	3
2	2	2	2	:		:		2	2	2				2	2	2	2	2	2	2	2	2	2	2	2	2	2	2
1	1	1	1	1	1	i	1	1	1	1	1	1 \ J		1	t	1	1	1	1	1	1	1	1	1	1	1	1	1
97	97	97	97	97	97	97	97	97	97	97	97	97 ¥r		97	97	97	97	97	97	97	97	97	97	97	97	97	97	97
	9	•		■	9	•		■				■	9			■		•	9	■	9	■	9	■			9	•
<			'				»		,0						,„		18	,9 20			'■'	/i	24»			"	78 79	
I
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
ED
Variability of core temperature
Seasonal variability (circannual rhythm)
Aging
37.0 r
o 22
OJ
Q.
£ o
CD
36.0
Summer /^
Winter
Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
Fine equilibrium of core temperature
INTAKE HEAT			LOSS HEAT	
PRODUCTION HEAT				
				OUTPUT HEAT
MUNI
E D
Transfer of heat in the organism
- primarily CONVECTION
- medium = blood
- to lower extent CONDUCTION
• Inner heat convection (between inner organs and skin)
• Outer heat convection - heat output
MUNI
9    Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University . . _ _
Heat production
- Metabolism: metabolic turnover ~ heat production (+10% BM ~ +1°C)
- Physical activity (muscle contractions) - rest vs. exercise (exercising muscles produce up to 70-90% of actual total heat production)
- Postprandial thermogenesis (food intake)
- Shivering thermogenesis (voluntary and non-voluntary shivering thermogenesis)
- Non-shivering thermogenesis (brown adipose tissue)
10   Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Heat intake and loss
- „passive" processes
- RADIATION (irradiation, IR, „touchless" heat sharing)
- CONVECTION
- CONDUCTION (touch)
- Dependent on temperature gradient shell (skin) - surrounding environment
MUNI
11   Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University . . _ _
Heat output (active loss)
- EVAPORATION
- perspiratio sensibilis = sweat production (1 I of evaporated sweat = - 2 428 kJ)
- perspiratio insensibilis = diffusion of water through skin and mucosa
- (RADIATION)
- (CONDUCTION)
- (CONVECTION)
12 Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Thermoregulation
- All processes aiming to keep core temperature within desired range
- Thermoregulatory behavior
- Social thermoregulation
13 Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Afferentation
- Central thermoreceptors - brain (core) temperature
- Temperature-sensitive neurons in anterior hypothalamus (area preoptica)
Peripheral thermoreceptors - skin (shell) temperature TRP channels
max .
14
Marie Nováková, Department of Physiology, Medicine, Masaryk University
Temperature ( C)
Adopted from:: https://doi.org/10.1016/bs.pmbts.2015.01.002
■ I
Si
. jo m
E E
■
MUNI
ED
Thermoregulatory center
- Anterior HYPOTHALAMUS (area preoptica)
- Integration of afferent information
- Modification of efferent pathways (vegetative, somatic) - impact on effector systems
- „set-point" vs. threshold temperature for effector systems
15 Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Effector systems of thermoregulation
- Behavior
- Skin circulation
- Sweat glands
- Skeletal muscles (voluntary movements, shivering thermogenesis)
- Horripilation (piloerection)
- Brown adipose tissue (non-shivering thermogenesis)
16 Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED
Cold-induced mechanisms
- Strategy: minimize heat loss
- Behavior: decrease body surface, dress up properly
- Vasoconstriction in skin, horripilation
- Inhibition of sweating
- Strategy: increase heat production
- Skeletal muscle: more frequent voluntary movements (behavior), shivering
- Non-shivering thermogenesis (brown adipose tissue, NA, (33R, lipolysis, lipoprotein lipase and thermogenin expression, mitochondrial uncoupling - UCP1)
- Increased appetite (increased food intake)
MUNI
17 Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University . . _ _
Heat-induced mechanisms
- Strategy: increase heat loss/output
- Skin vasodilation
- Increase sweating (evaporation)
- Increase ventilation Strategy: decrease heat production
- Behavior: search for shadow, light dress
- Inactivity, apathy
- Loss of appetite (decreased food intake)
18   Marie Nováková, Department of Physiology, Faculty of Medicine, Masaryk University
MUNI
MED