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

Question 1

Words to include in heat balance

Answer 1

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

Question 2

Words to include in the effect of the environmental temperature

Answer 2

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

Question 3

Topics to include in the essay

Answer 3

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

Question 4

The heat balance

Forms of heat balance

Answer 4

• 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

Question 5

The heat balance

Importance of heat exchange

Answer 5

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

Question 6

The heat balance

Influence of age on body temperature

Answer 6

• 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

Question 7

The heat balance

Equation

Answer 7

• 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

Question 8

The heat balance

Neural control

Answer 8

• 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

Question 9

The effects of environmental temperature

Defense against cold

Answer 9

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)

Question 10

Effects of the environmental temperature

Defense against heat

Answer 10

• ​​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