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Physiology > Thermoregulation > Flashcards

Thermoregulation Flashcards

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
Q

Heat exchange occurs via…

A
  • Radiation
  • conduction
  • evaporation
  • Convection

from blood

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26
Q

Describe heat loss at the skin

A
  1. Air warmed by skin becomes lighter
  2. This air leaves the area of the skin
  3. Replaced by cold air
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27
Q

What is an important element of environmental temperature adaptation?

A
  • The thickness of adipose layer

Adipose/muscle are poor conductors

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28
Q

Calculate the rate of heat-loss by radiation/convection

A
  • A = surface area*
  • t2-t1 = Thermal gradient*
  • k = Constant (depends on the given material)*
  • l = Distance the heat covers*
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29
Q

Heat reception is accomplished by…

A

Central and peripheral cold and heat sensors

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30
Q

Simultaneous activity of heating and cooling areas adjusts…

A
  • Heat loss
  • Heat conservation
  • Heat production
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31
Q

Give the forms of heat loss

A
  • Conduction
  • Radiation
  • Evaporation (sensible/insensible)
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32
Q

In a well-defined temperature range, BMR is…

A

Constant

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33
Q

Animals prefer a … range for a thermoneutral zone

A

Narrow

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34
Q

What is expressed in this figure?

A

Heat balance

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35
Q
A

Optimal temperature

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36
Q
A

Cold stress

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37
Q
A

Heat stress

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38
Q
A

Frostbite/freezing

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39
Q
A

Heat shock

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40
Q
A

Lower critical temperature

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41
Q
A

Upper critical temperature

42
Q
A

Adjustable zone

43
Q
A

Thermoneutral zone

Vasomotor, behavioural, pilomotoric activity

44
Q

Give the order of defences against cold

A
  1. Behavioural heat preservation
  2. Increased muscular activity/Shivering
  3. Chemical thermogenesis (Non-shivering)
  • Metabolic heat production
45
Q

What causes uncoupling of oxidative phosphorylation in the mitochondria?

A

Change in the proton flux

(Needed for ATP synthesis)

46
Q

Effect of thyroid hormones on body temperature

A
  • Slow but prolonged effect
  • BMR increase
  • No. mitochondria increase
  • Thermogenin increase
  • Na+/K+ ATPase activity increase
47
Q

Brown adipose tissue defence against cold

A
  • 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
Q

The steps of heat production in brown tissue

49
Q

Brown adipose cycle: ‘Sympathetic activation’

A
  1. Permeability of adipose increases to Na+ and K+ ions
  2. Depolarisation
50
Q

Brown adipose cycle: ‘Futile cycle’

A
  1. Increased Na+/K+ pump action
  2. Heat production
51
Q

Brown adipose cycle: ‘cAMP production’

A
  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
Q

Defence against heat

A
  • Behavioural
  • ‘Dry’ heat loss
    • Conduction
    • Convection
    • Radiation
  • ‘Humid’ heat loss
53
Q

‘Humid’ heat loss

A
  • Perspiratio insensibilis
    • Diffusion from the alveolar, skin and oral mucous membrane surface
      • Panting
  • Perspiratio sensibilis
    • Sweating
54
Q

How much energy is released in 1g of sweat through evaporation?

55
Q

Evaporation might account to …% of heat loss

56
Q

Panting

A
  • Vapour release during expiration and inspiration
  • Orally, evaporative heat-loss occurs only during expiration
  • Panting frequency = Resonance-frequency of the thoracic cavity
57
Q

Panting is found in which species?

A
  • Dog
  • Cat
  • Sheep
  • Birds
58
Q

Gular flutter

A
  • In birds
  • Lowering + rising the larynx at high frequency
  • Effective at evaporation
59
Q
60
Q
61
Q
62
Q
A
  • Rabbit
  • Bird
  • Guinea pig
63
Q

% heat production: Brain

64
Q

% heat production: Heart muscle

65
Q

% heat production: Skeletal muscle

66
Q

% heat production: Liver

67
Q

% heat production: Kidney

68
Q

% heat production: Skin

69
Q

Circulation in heat

A
  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
Q

Circulation in cold

A
  1. Precapillary sphincters constrict - AVA system becomes closed
  2. Deep major veins dilate, superficial veins shrink - Heat returns to the core
71
Q

Examples of countercurrent heat exchange

A
  • In heat:
    • In the leg of birds
  • In cold:
    • In the head
    • In the testicles
72
Q

Countercurrent exchange in the head

A
  • 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
Q
A

Hypothalamus

Thermostat set point

74
Q
A

Execution

  • Heat production
  • Behaviour
  • Heat dissipation
75
Q
A

‘Current value’

76
Q
A

Sensors/’Thermometers’

  • Peripheral:
    • Cold receptors
    • Heat receptors
  • Central:
    • Hypothalamic
    • Receptor field
77
Q

The peripheral and central receptors sense the ‘current value’ and forward it as…

A

An afferent neural signal to the hypothalamic centre

78
Q

Hypothermia

A
  • Homeothermia ceases
  • Metabolism slows
  • Heart + resp. frequency drops
79
Q

What follows hypothermia?

A
  • Circulatory failure
  • Hypercapnia
  • Hypoxia
  • Digestive disorders
  • Renal failure
  • Fainting
  • VF
80
Q

Why are newborns and clipped sheep more prone to hypothermia

A
  • Cold environmental temp.
  • Humid skin surface

Enhanced by strong wind

81
Q

Artificial hypothermia at surgical interventions

A

Adequate + expert artificial respiration is important

82
Q

Hyperthermia

A
  • Decreased BMR
  • Excessive flow of blood into blood vessels
    • Corruption of circulation (‘Overheating shock’)
83
Q

What follows hyperthermia?

A
  • Hypercapnia
  • Loss of water + salts
  • Hypovolemia
  • Muscle seizures
84
Q

Warm blood damages…

A
  • Respiratory + circulatory centres
  • CNS
85
Q

Animals bear hyperthermia harder because…

A

their body temperature is closer to the upper limit of durable temperature

86
Q

Most sensitive species to hyperthermia

87
Q

Fever

A
  • Regulated hyperthermia
  • Induced by infection/inflammation
88
Q

Pyrogen

A
  • Endotoxins of gram-negative bacteria
  • Polysaccharides
  • Membrane debris
  • Lipopolysaccharide fragments
89
Q

Process of fever

A
  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
Q

Effect of fever on the hypothalamus

A
  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
Q

Acclimatisation

A
  • ‘Relatively slow’ adaptation to extreme environmental temp.
  • Can shift lower or higher critical temp.
92
Q

Morpho-functional changes in cold

A
  • Thickening of fur + Adipose thickening
  • Calorigenic hormones:
    • Increased thyroid hormone
    • Increased glucocorticoids
    • Increased BMR
  • Superficial vasoconstrictor mechanisms of the skin
93
Q

Morpho-functional changes in warm

A
  • Decreased thickness of insulating layers
  • The dominance of heat dissipating mechanisms
    • Activate sweat glands
    • Increase respiratory muscle activity
    • Superficial vasodilation of skin
94
Q

Enzyme effects on acclimatisation

A
  • Kinetic changes of reactions
  • Appearance of new enzyme isoforms → enzyme induction
  • Changes metabolic enzymes
  • Suitable for long term increase/decrease of BMR
95
Q

Cellular thermogenesis

A

Two mechanisms:

  1. Mitochondrial heat production → Brown adipose tissue
  2. ‘Heating cells’ - Modified muscle cells (Based on fish)
96
Q

Brown adipose thermogenesis

A
  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
Q

Heater cells/ futile cycle overview

A

Found in certain species/Young animals with large brown adipose

  • Temp. of CNS of some fish = temp. of homeothermic animals
98
Q

How do heater cells function?

A
  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
Q

Futile cycle

A
  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
Q

Malignant hyperthermia

A

Stress sensitivity/Pathological hyperthermia

  • Inherited on single locus:
    • H antigen
    • Phospho-hexo-isomerase (PHI)
    • Defective ryanodine receptor
101
Q

Malignant hyperthermia was used for…

A

Clarifying the thermogenic role of Ca2+ pumping proteins of the SR membrane

102
Q

How does malignant hyperthermia occur?

A
  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

Physiology (18 decks)

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