Topic 66 - The heat balance, and the effect of the environmental temperature Flashcards

1
Q

Words to include in heat balance

A

Forms of heat balance

  • Poikilothermic
    • Depends on external temperature
    • Transiently poikilothermic
      • Hibernating animals
        • CNS previous core temperature
    • Inactivated by higher environmental temperature
      • Snakes
    • Aestivation
      • Summer inactivation period
  • Heterothermic
    • Independent of external temperature
    • Poikilothermuc under certain conditions
      • Transiently poikilothermic
        • Hibernating animals
  • Homeothermic
    • Independent of environmental temperature at all times
      • Core temperature
    • Domestic mammals

Importance of heat exchange

  • One way heat exchange
    • Low efficiency
    • Looping heat exchange
      • Prevents heat loos through extrtimities
  • Counter-current heat exchange
    • More efficient
    • Heat in warm branch transferred to cold branch
      • Exchange between deep arterial and venous system
    • Domestic animals

Influence of age on body temperature

  • Time of day
  • Food intake / food quality
  • Moltility
  • Muscle activity
  • Sexual cycle
  • Gravidity
  • Parturition
  • Alters:
    • Core temperature
    • Peripheral temperature
    • Higher metabolic rate in young animals
      • Higher temperature gradient against the environment
      • Higher speed of heat loos
  • Thermoneutral zone
    • Consume least O2
    • Zone narrow with age

Heat balance equation

  • Ht = Hm + Hc + Hr + He + Hs
    • Ht: normal amount of heat of the body
    • Produced heat:
      • Hm: metabolically produced
      • Hs: stored in chemical bonds
    • Exchange heat:
      • Hc: convection
      • Hr: radiation
        • He: evaporation
  • Hypothalamic control
    • Maintaining body temperature
    • Central and peripheral cold and heat sensors
    • Heating area
    • Cooling area

Defense against cold

  • First line of defenseHeat conservation
    • Diminishing heat-loss
  • Muscular activity ↑
    • Tonic (isometric) or shivering ↑
  • Chemical (non-shivering) thermogenesis
  • Brown adipose tissue (compared to white adipose tissue)
    • Foamy
    • intensive blood supply
    • Mitochindria
  • Heat production in brown adipose:
    • Cold
    • Sympathetic activation (epinephrine, norepinephrine)
    • Futile cycle
    • cAMP production
    • Lipase activity ↑
    • FFA level ↑
      • Transport to other organs
        • Oxidation
      • Oxidation in mitochondria

Defense against heat

  • Humid heat loos: evaporation
    • Persipiratio sensibilis
      • Sweating
        • Location of sweat glands in different species
    • Persipiratio insensibilis
      • Diffusion from surface of alveoli, skin and oral mucous membranes
        • Panting
  • Panting:
    • Evaporation (water loss)
    • Advantage: Influence degree of heat loss
    • Disadvantage: Alkalosis and consume energy
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2
Q

Words to include in the effect of the environmental temperature

A

Hyopthermia

  • Below controllable range
  • Metabolism ↓
  • Heat / respiratory frequency ↓
  • Circulatory failure
    • Hypercapnia
      • Too much CO2 in blood
    • Hypoxia
      • Too little dissolved CO2
  • Disorders of:
    • Digestion
    • Absorption
    • Kidney functions
  • Fainting
  • Ventricular fibrillations

Hyperthermia

  • Insufficient operation of heat dissipating mechanism
  • Metabolism ↓
  • Corruption of circulation → overheating shock
  • Hypercapnia
  • Hypervolemia
  • Loss of salts and water
  • Muscle seizure
  • Fever

Morpho-functional changes

  • In cold:
    • Thickening of fur coat
    • Subcutaneous adipose tissue ↑
    • Calorigenic hormones
      • Thyroid hormone ↑
      • Glucocorticoids ↑
      • Metabolic rate ↑
    • Superficial vasoconstrictor mechanism of skin
      • a/v shunt
  • In heat:
    • Thickness and density of insulation layers ↓
    • Activation of sweat glands
      • Aldosterone effects
    • Respiratory musculature ↑
    • Superficial vasodilation of skin
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3
Q

Topics to include in the essay

A
  1. The heat balance
    • Forms of heat balance (in different species)
    • Importance of heat exchange
    • Influence of age on body temperature
    • Equation
    • Maintainance of constant body temperature
      • Defense against cold
        • Heat production in brown adipose
      • Defense against heat
        • Panting
  2. Effect of environmental temperature
    • Hypothermia
    • Hyperthermia
    • Morpho-functional changes
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4
Q

The heat balance

Forms of heat balance

A
  • Regarding their heat balance animals can be divided into three major groups:
    1. Poikilothermic
      • Body temperature depends on external temperature
      • Hibernating animals are transitiently polikilothermic
        • ​CNS is the only one which has the previous core temperatrue
      • Animals can be inactivated by higher environmental temperature (several snakes)
        • Aestivation: summer inactivation period
    2. Heterothermic
      • Body temperature independs on external temperatur
      • May act poikilothers under certain conditions
        • Transiently poikilothermic (hibernating animals)
    3. Homeothermic
      • Body temperature independent of environmental temperature at all times
        • Posession of a core temperature
      • Core temperature is diagnostic parameter, its value is altered by:
        • Time of day
        • Feed intake
        • Muscular activity
        • Sex
        • Age
      • All domestic mammals
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5
Q

The heat balance

Importance of heat exchange

A
  1. One way heat exchange
    • Low efficiency
    • Looping heat exchange
      • Prevents heat loss through extremities in contact with ground
  2. Counter-current heat exchange
    • ​​More efficient than unidirectional heat exchange
    • Heat is warm branch transfered to cold branch
      • Indentical temperature in both branches
      • Exchange between deep arterial and venous system
    • Domestic animals
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6
Q

The heat balance

Influence of age on body temperature

A
  • Alters mostly the core and peripheral temperature
  • Younger animals: higher body temperature due to higher metabolic rate
    • Higher temperature gradient against the environment
    • Higher speed of heat loss
  • Thermoneutral zone:
    • Value at which the animals consume least O2
    • Zone narrows with age

Figure: oxygen consumption of chickens of different ages

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7
Q

The heat balance

Equation

A
  • Ht: normal amount of heat of the body
    1. Produced heat:
      1. ​Hm: metabolically produced
      2. Hs: stored in chemical bonds
    2. Exchanged heat:
      1. ​Hc: convection
      2. Hr: radiation
      3. He: evaporation
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8
Q

The heat balance

Neural control

A
  • Hypothalamic control is the basis of maintaining body temperature:
    • Central and peripheral cold and heat sensors accomplish the heat reception
    • The center can be divided into heating and cooling areas
      • ​Simultaneous activity of these two centers adjust the heat loss
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9
Q

The effects of environmental temperature

Defense against cold

A
  1. Heat conservation: ​Diminishing the heat loss​
    • Animals living in groups cuddle up to each other diminishing the surface are of heat loss
  2. Muscular activity ↑
    • ​Increase tonicity (isomtric) or shivering
  3. Chemical (non-shivering) thermogenesis
    • If the two above-mentioned forms are not able to maintain the constant body temperature
  • Brown adipose tissue compared to white adipose tissue:
    • Foamy
    • Intensive blood supply
    • Many mitochondria

Hypothermia

  • Body temperature decreases below the controllabele range
  • Metabolism ↓
  • Heart / respiratory frequency ↓
  • Circulation failute
    • ​Hypercapina (too much CO2 in blood)
    • Hypoxia (too little dissolved CO2)
  • Disorders of:
    • Digestion
    • Absorption
    • Kidney functions
  • Fainting
  • Ventricular fibrillations

Morpho-functional changes

  • Thickening of fur coat and subcutaneous adipose tissue
  • Calorigenic hormones increases secretion:
    • Thyroid hormones ↑
    • Glucocorticoids ↑
    • Metabolic rate ↑
  • Superficial vasoconstrictor mechanism of sikn (a/v shunt)
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10
Q

Effects of the environmental temperature

Defense against heat

A
  • ​​Humid heat-loss: evaporation:
    1. ​Perspiratio insensibilis
      • ​Panting by diffusion from the alveoli, skin and oral mucous membranes
    2. Perspiratio sensibilis
      • ​Sweating
  • Panting:
    • Advantage: animal can actively influence the degree of heat-loss
    • Disadvantage: excessive panting can cause alkalosis and consumes energy

Hyperthermia:

  • Insufficient operantion of heat dissipating mechanisms:
    • Metabolism ↓
    • Corruption of circulation → overheating shock
    • Hypercapnia
    • Hypeovolemia
    • Water and salt loss
    • Muscle sizure

Morpho-functional changes:

  • Thickness and density of isulation layers ↓
  • Activation of sweat glands
    • Aldosterone effect
  • Respiratory muscles ↑
  • Superficial vasodilation of skin
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