Topic 67 - Heat balance regulation Flashcards

1
Q

Words to include

A

Defense against cold

  • Heat 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
  • Sympathetic excitation
    • Adrenaline / noradrenaline effect
    • Thyoxine effect
      • Uncoupling of oxidative phosphorylation by thermogenins
  • Calorigenic effect of thyroid hormones
    • Heat production prolonged effect
    • BMR
    • Number of mitochondria
    • Amount of thermogenin
    • Activity of Na+/K+ pump
  • Brown adipose tissue
    • Foamy
    • Fine IC granular content
    • Intensive blood supply
    • Many mitochondria
      • High humber of cyochrome-oxidase
    • α and β-adrenergic receptors on their surface
  • Morpho-functional changes against cold
    • Thickening of fur and subcutaneous tissue
    • Secretion of calorigenic hormones ↑:
      • Thyroid hormones
      • Glucocorticoids
      • Metabolic rate ↑
    • Superficial vasoconstriction (a/v shunt)

Defense against heat

  • Humid heat loos: evaporation
    • Persipiratio sensibilis
      • Sweating
    • 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
  • Behaviroal defense reactions
  • Dry heat loss
  • Conduction
    • Direct contact with surrounding objects
  • Convetion
    • Air/water touching body
  • Morpho-functional changes against heat:
    • Thickness and density of insulating layers ↓
    • Heat dissipating mechanisms
    • Vasodilation

Circulation and heat balance

  • Hypothalamic center
    • Control body temperature
  • Circulation in heat:
    • Superficial skin layer
      • Precapillary sphincters open
    • Deep system:
      • Major veins contract
      • Superficial veins dilate
  • Circulation in cold:
    • Superficial skin layer
      • Precapillary sphincters close
    • Deep system:
      • Major veins dilate
      • Superficial veins contract

Specialized structures

  • Defense against major heat loss through limbs
    • Looping heat exchange
      • Warm blood flowing towards limbs can get cool
        • Ø temperature gradient among body and environment
  • Counter current heat exchange
    • In hot
      • In the leg of birds (rete mirabile)
    • In cold
      • In head (rete of carotis)
      • In testicles (rete testis)
  • Heat tolerant species
    • Sheep
    • Cooling of brain and CNS

Central thermoregulation

  • Hypothalamic center
    • Thermostat
    • Set value of core temperature
    • Effector system
      • Maintain body temperature near to hypothalamic set-point
  • Receptors
    • Peripheral
    • In organs
  • Afferentation
  • Hypothalamic termostat
  • Efferentation
    • Somatic
    • Vegetative
    • Hormonal
  • Hypothermia
    • 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
  1. Fever
  2. Fever is a regulated hyperthermia
    • Induced by:
      • Infections
      • Inflammations
      • Tissue destruction
  3. Exogenous pyrogens get into organism
  4. Macrophage activation
  5. Formation of interleukin-1 & 6
  6. Direct stimulation of hypothalamic heat center by local prostaglandin (PGE1) release
  • Pyrogens
    • Endotoxins of Gram-negative bacteria
    • Heat stable polysaccharides
    • Membrane derbis
    • Lipopolysaccharide fragments
  1. Pyrogens set hypothalamic set point to a higher temperature
  2. Incude heat production and heat conserving processes
    1. Shivering
  3. Temperature stabilizes at a higher value
  4. Removing pyrogens → set point drops back to previous normal value
    1. Sweating (cooling mechanism starts to work)

Acclimatization

  • Adaption
    • Shift to lower/higher critical temperature
      • Shift of thermoneutral zone
  • Morpho-functional changes in heat:
    • Thickness and density of insulating layers ↓
    • Dominance of heat dissipating mechanisms
      • Activation of sweat glands
      • Activity of respiratory muscles ↑
      • Superficial vasodilation of skin
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2
Q

Topics to include in the essay

A
  1. Maintaining constant body temperature
    • Defense against cold
      • Sympathetic excitation
      • Calorigenic effect of thyorid hormones
      • Brown adipose tissue
      • Morpho-functional changes against cold
      • Hypothermia
    • Defense against heat
      • Panting
      • Morpho-functional changes against heat
      • Hyperthermia
  2. Circulation and heat balance
    • Circulation in heat
    • Circulation in cold
  3. Specialized structure
    • Limbs (defense against heat-loss)
    • Heat tolerant species (sheep)
  4. Central thermoregulation
  5. The fever
  6. Acclimatization
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3
Q

Defense against cold

A
  1. Heat conservation: diminishing heat-loss
    1. Animals living in groups cuddle up to each other diminishing the surface are of heat loss
  2. Muscle activity ↑
    1. ​Tonicity (isometric) or shivering ↑
  3. Chemical (non-shivring) thermogenesis
    1. If the two above-mentioned forms are not able to maintain the constant body temperature

​Sympathetic excitation

  • Effect of adrenaline / noradrenaline
  • Long term thyroxine effects
    • (Uncoupling of oxidative phosphorylation by thermogenin)

Calorigenic effect of thyroid hormones

  • Prolonged effect on heat production
  • Basic metabolic rate (BMR)
  • Number of mitochondria
  • Increase energy consumption and heat production
  • Amount of thermogenin
  • Activity of Na+/K+ pump

Brown adipose tissue

  • Foamy
  • Fine IC granular content
  • Intensive blood supply
  • Many mitochondria
  • High number of cytochrome-oxidase
  • α and β-adrenergic receptors on their surface

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)

Figure: heat production in brown adipose

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4
Q

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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5
Q

Circulation and heat balance

A
  • Thermal conductivity of tissues is lower, therefore are heat transported between the organs, inner body parts and the body surface
  • Thermoneutral zone
  • Circulation in heat:
    • Superficial skin layer:
      • Precapillary sphincters open
    • Deep system:
      • Major veins contract
      • Superficial veins dilate
  • Circulation in cold:
    • Superficial skin layer:
      • Precapillary sphincters close
    • Deep system:
      • Major veins dilate
      • Superficial veins contract
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6
Q

Specialized structures in different species

A
  • Defense against major heat loss through limbs:
    • Looping heat exchange
    • Warm blood flowing towards the limbs can get cool to a degree that close to the ground there is hardly any temperature gradient among the body and the environment
    • Polar animals that are exposed to extremely low temperatures has a much higher proportion of unsaturated fatty acids in the cells of the limbs compared to other body parts
  • Heat tolerant species (sheep) have special circulatory units
    • Ensuring cooling of brain and CNS
      1. ​​Plexus of nasal cavity: cools blood by panting
      2. Cooled venous blood gets to ring of Willsius
      3. Blood of ascending a. carotis gets cooled by heat exchang before reaching the brain
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7
Q

Central thermoregulation

A
  • The hypothalamic center as a thermostat determines a certain set point value for the core temperature
  • The effector systmes are used to maintain body temperature near to the hypothalamic set-point
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8
Q

The fever

A
  • Pyrogens:
    • ​Endotoxins of Gram-negative bacteria
    • Heat stable polysaccharides
    • Membrane derbis
    • Lipopolysaccharide fragments
  1. At the beginning of fever process the pyrogenic substance sets the hypothalamic set point to a higher temperature
  2. This induces heat production and heat conserving processes (shivering)
  3. As the current value reaches the set point the fever temperature becomes stabilized at a higher value
  4. After removing the pyrogenic substance the set point drops back to the previous normal value:
    • Cooling mechanisms start to work (sweating) and the fever becomes solved
  5. Feves is regulated hyperthermia
    1. Influenced by:
      1. Infection
      2. Inflammations
      3. Tissue destruction
  6. Exogenous pyrognes get into the organism
  7. Macrophage activation
  8. Formation of:
    1. Interleukin-1
    2. Interleukin-6
  9. Direct stimulation of hypothalamic heat center by local prostaglandin (PGE1) release
  10. Hypothalamic regulation
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9
Q

Acclimatization

A
  • Adaptation can shift the lower or higher critical temperature (shift of the thermoneutral zone) to higher or lower levels
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