Physiology > Thermoregulation > Flashcards

Thermoregulation Flashcards

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1
Q

Thermoneutral zone

A

The thermal zone which is suitable for the subjective demands of animals

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2
Q

Centre of thermoregulation

A

Hypothalamus

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3
Q

Animals can be divided into which groups of thermoregulation

A
  • Poikilothermic animals
  • Heterothermic animals
  • Homeothermic animals
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4
Q

Poikilothermic animals

A

Body temp. changes depending on environmental temp.

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5
Q

Heterothermic animals

A
  • Body temp. independent of environmental temp.
  • Some time behave as poikilothermic animals
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6
Q

Homeothermic animals

A
  • Body temp. independent of environmental temp.
  • Permanently
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7
Q

Domestic animals belong to which thermogenic group?

A

Homeothermic animals

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8
Q

Core temperature is affected by…

A
  • Time of day
  • Feed intake
  • Muscular activity
  • Sex
  • Age
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9
Q
A

Beginning of hibernation

  • Metabolic rate decrease
  • Body temperature decrease
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10
Q
A

Awakening

  • Body temperature increase
  • Metabolic rate increase
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11
Q

Hibernating animals becomes transiently…

A

Poikilothermic

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12
Q

During a 3-month hibernation period….

A
  • CNS is the only system that remains at the core temperature
  • Achieved by special heating elements surrounding the brain
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13
Q

Hibernation is interrupted by…

A
  • Awakening phase (for a few hours)
  • This happens every 2-3 weeks
  • BMR rises 120-140%
  • Rapid warming
  • Feeding, micturate, defecate
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14
Q

Micturation

A

Urination

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15
Q

Aestivation

A
  • ‘Hibernation’ in high environmental temperatures
  • In the middle of summer, inactive metabolic condition
  • Avoid dangers caused by dryness + heat
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16
Q

Torpor

A
  • Animal is in a still, rigid state
  • Observed in animals that cannot provide energy reserves at night
  • Decrease of metabolic speed
  • Body temp. = near environmental temp.
  • Heat of the sun + increased BMR activates the animal again

E.g Hummingbird

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17
Q

The temperature of body parts

A
  • Limbs are colder than the core
  • The ratio of unsaturated fatty acids in the limbs is higher in polar animals
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18
Q

Coolin of the limbs is inhibited by…

A

Efficient heat exchange systems

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19
Q

One-way heat exchanger

A
  • Low efficiency
  • Effluent temp. gives the average of incoming temps.
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20
Q

Looping heat-exchange

A
  • Most effective defence against heat loss
  • Between the body and the ground
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21
Q

Counter-current heat exchanger

A
  • More effective than unidirectional heat exchange
  • Heat flowing out can be almost fully transferred in
  • Temp of substance leaving warm branch = Temp of substance entering the cold branch
  • Observed in domestic animals - Deep blood vessel systems
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22
Q

Influence of age on body temperature

A
  • High temp in young animals - Higher BMR
  • Thermoneutral zone becomes narrower as age increases
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23
Q

Thermoneutral zone

A

Value where animals consume the least amount of oxygen

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24
Q

Heat balance

A
  • Occurs in normal conditions
  • Total body heat (Ht) divided into:
    • Produced heat
      • Hm (Metabolic)
      • Hs (Chemical)
    • Exchanged heat
      • Hc (Convection)
      • Hr (Radiation)
      • He (Evaporation)
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25
Heat exchange occurs via...
* Radiation * conduction * evaporation * Convection from blood
26
Describe heat loss at the skin
1. Air warmed by skin becomes lighter 2. This air leaves the area of the skin 3. Replaced by cold air
27
What is an important element of environmental temperature adaptation?
* The thickness of adipose layer Adipose/muscle are poor conductors
28
Calculate the rate of heat-loss by radiation/convection
* A = surface area* * t2-t1 = Thermal gradient* * k = Constant (depends on the given material)* * l = Distance the heat covers*
29
Heat reception is accomplished by...
Central and peripheral cold and heat sensors
30
Simultaneous activity of heating and cooling areas adjusts...
* Heat loss * Heat conservation * Heat production
31
Give the forms of heat loss
* Conduction * Radiation * Evaporation (sensible/insensible)
32
In a well-defined temperature range, BMR is...
Constant
33
Animals prefer a ... range for a thermoneutral zone
Narrow
34
What is expressed in this figure?
Heat balance
35
Optimal temperature
36
Cold stress
37
Heat stress
38
Frostbite/freezing
39
Heat shock
40
Lower critical temperature
41
Upper critical temperature
42
Adjustable zone
43
Thermoneutral zone ## Footnote *Vasomotor, behavioural, pilomotoric activity*
44
Give the order of defences against cold
1. Behavioural heat preservation 2. Increased muscular activity/Shivering 3. Chemical thermogenesis (Non-shivering) * Metabolic heat production
45
What causes uncoupling of oxidative phosphorylation in the mitochondria?
Change in the proton flux | (Needed for ATP synthesis)
46
Effect of thyroid hormones on body temperature
* Slow but prolonged effect * BMR increase * No. mitochondria increase * Thermogenin increase * Na+/K+ ATPase activity increase
47
Brown adipose tissue defence against cold
* Located near the interscapular region/abdominal cavity * Blood supply, many mitochondria * High cytochrome oxidase (brown colour) * Fat is oxidised in these adipose cells * Have alpha-/beta- adrenergic receptors
48
The steps of heat production in brown tissue
49
Brown adipose cycle: 'Sympathetic activation'
1. Permeability of adipose increases to Na+ and K+ ions 2. Depolarisation
50
Brown adipose cycle: 'Futile cycle'
1. Increased Na+/K+ pump action 2. Heat production
51
Brown adipose cycle: 'cAMP production'
1. cAMP increases lipase activity 2. Increases FFA in cell 3. Most FFA oxidised by mitochondria → Heat 4. Other FFA goes to organs → Further heat production
52
Defence against heat
* Behavioural * 'Dry' heat loss * Conduction * Convection * Radiation * 'Humid' heat loss
53
'Humid' heat loss
* Perspiratio insensibilis * Diffusion from the alveolar, skin and oral mucous membrane surface * Panting * Perspiratio sensibilis * Sweating
54
How much energy is released in 1g of sweat through evaporation?
0.58kcal
55
Evaporation might account to ...% of heat loss
80%
56
Panting
* Vapour release during expiration and inspiration * Orally, evaporative heat-loss occurs only during expiration * Panting frequency = Resonance-frequency of the thoracic cavity
57
Panting is found in which species?
* Dog * Cat * Sheep * Birds
58
Gular flutter
* In birds * Lowering + rising the larynx at high frequency * Effective at evaporation
59
* Eq * Ru * Su
60
* Ca. * Ho.
61
* Fe * Rat
62
* Rabbit * Bird * Guinea pig
63
% heat production: Brain
18%
64
% heat production: Heart muscle
12%
65
% heat production: Skeletal muscle
20%
66
% heat production: Liver
20%
67
% heat production: Kidney
7%
68
% heat production: Skin
5%
69
Circulation in heat
1. Precapillary sphincters open - AVA system opens, increasing blood to superficial areas 2. Major deep veins contract, superficial ones dilate - Heat barely returns to the core 1 + 2 together are very effective at head dissipation
70
Circulation in cold
1. Precapillary sphincters constrict - AVA system becomes closed 2. Deep major veins dilate, superficial veins shrink - Heat returns to the core
71
Examples of countercurrent heat exchange
* In heat: * In the leg of birds * In cold: * In the head * In the testicles
72
Countercurrent exchange in the head
* Some animals have circulatory units ensuring CNS cooling 1. Blood in the nasal venous plexi cooled by panting 2. Cooled blood → basal cranial system of Willisius 3. Blood of *a.* *carotis* is cooled before reaching the brain
73
_Hypothalamus_ Thermostat set point
74
_Execution_ * Heat production * Behaviour * Heat dissipation
75
'Current value'
76
_Sensors/'Thermometers'_ * Peripheral: * Cold receptors * Heat receptors * Central: * Hypothalamic * Receptor field
77
The peripheral and central receptors sense the 'current value' and forward it as...
An afferent neural signal to the hypothalamic centre
78
Hypothermia
* Homeothermia ceases * Metabolism slows * Heart + resp. frequency drops
79
What follows hypothermia?
* Circulatory failure * Hypercapnia * Hypoxia * Digestive disorders * Renal failure * Fainting * VF
80
Why are newborns and clipped sheep more prone to hypothermia
* Cold environmental temp. * Humid skin surface ## Footnote *Enhanced by strong wind*
81
Artificial hypothermia at surgical interventions
Adequate + expert artificial respiration is important
82
Hyperthermia
* Decreased BMR * Excessive flow of blood into blood vessels * Corruption of circulation ('Overheating shock')
83
What follows hyperthermia?
* Hypercapnia * Loss of water + salts * Hypovolemia * Muscle seizures
84
Warm blood damages...
* Respiratory + circulatory centres * CNS
85
Animals bear hyperthermia harder because...
their body temperature is closer to the upper limit of durable temperature
86
Most sensitive species to hyperthermia
Swine
87
Fever
* Regulated hyperthermia * Induced by infection/inflammation
88
Pyrogen
* Endotoxins of gram-negative bacteria * Polysaccharides * Membrane debris * Lipopolysaccharide fragments
89
Process of fever
1. Pyrogens get into the organism 2. Macrophage activation 3. Formation of interleukin-1 and -6 4. Stimulation of hypothalamic heat centre by PGE1 release 5. Hypothalamic regulation
90
Effect of fever on the hypothalamus
1. Setpoint increased to higher temp. 2. Heat production/conservation processes 3. As current value reaches set point, fever temp. becomes stabilsied 4. Pyrogenic substance removed 5. Set point drops to the previous norm 6. Cooling mechanisms (sweating)
91
Acclimatisation
* 'Relatively slow' adaptation to extreme environmental temp. * Can shift lower or higher critical temp.
92
Morpho-functional changes in _cold_
* Thickening of fur + Adipose thickening * Calorigenic hormones: * Increased thyroid hormone * Increased glucocorticoids * Increased BMR * Superficial vasoconstrictor mechanisms of the skin
93
Morpho-functional changes in _warm_
* Decreased thickness of insulating layers * The dominance of heat dissipating mechanisms * Activate sweat glands * Increase respiratory muscle activity * Superficial vasodilation of skin
94
Enzyme effects on acclimatisation
* Kinetic changes of reactions * Appearance of new enzyme isoforms → enzyme induction * Changes metabolic enzymes * Suitable for long term increase/decrease of BMR
95
Cellular thermogenesis
Two mechanisms: 1. Mitochondrial heat production → Brown adipose tissue 2. 'Heating cells' - Modified muscle cells (Based on fish)
96
Brown adipose thermogenesis
1. Thyroid hormones 2. _Thermogenin_ + UCP (uncoupling protein) settles in the inner membrane of mitochondria 3. Epinephrine → free fatty acids generated in cells 4. Open thermogenin channel 5. H+ enters channel → + O2 → Water formation 6. No ATP synthesis → Only heat produced
97
Heater cells/ futile cycle overview
Found in certain species/Young animals with large brown adipose * Temp. of CNS of some fish = temp. of homeothermic animals
98
How do heater cells function?
1. Ca2+ pump of SR functions without muscle contraction 2. Modified ryanodine receptor allows Ca2+ leakage from SR 3. This continuously activates Ca2+ pumps → Heat production
99
Futile cycle
1. Skeletal muscle → Epinephrine + thyroxine stimulation 2. increases Ca2+ pump function 3. Increased Na+ permeability gears up Na+/K+ pump function 4. The pump is abused
100
Malignant hyperthermia
Stress sensitivity/Pathological hyperthermia * Inherited on single locus: * H antigen * Phospho-hexo-isomerase (PHI) * Defective ryanodine receptor
101
Malignant hyperthermia was used for...
Clarifying the thermogenic role of Ca2+ pumping proteins of the SR membrane
102
How does malignant hyperthermia occur?
1. Produces defective ryanodine channel SR (H antigen) 2. Lysine produced instead of arginine → Channels are leaky to Ca2+ 3. Intensive pumping back of Ca2+ to the SR 4. Extreme heat production → Hyperthermia Proves that muscle is _thermogenic_ as well as contractile
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