Thermoregulation

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Thermoregulation

• Homeostasis

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Temperature Extremes

• Humans are subjected to vast changes in
  environmental temperatures
• Enzymes operate over a very narrow range of
  temperatures
• Failure to control body temperature can result in
  physiological changes damage
• The body has several mechanisms to maintain body
  temperature
• Thermoregulation

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Temperature

• Core temperature
• most important body temperature
• temperature of organs in major cavities
• rectal temperature gives best estimation
• Shell temperature
• temperature closer to surface
• skin oral temperatures

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Mechanisms of Heat Transfer

• Radiation
• Conduction
• Convection
• Evaporation

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Evaporation

• water changes from liquid to vapor

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Thermoregulation Homeostasis

• Control Center
• preoptic area of hypothalamus
• Receptors
• in skin
• Effectors
• eccrine sweat glands blood vessels

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Mechanisms for Heat Loss

• Skin receptors note increase in
  temperature?messate sent to preoptic nucleus
  ?heat loss center (also in the hypothalamus)
  stimulated?sets off series of events to produce
  heat loss
• inhibition of vasomotor center?peripheral
  vasodilation?warm blood flows to skins surface?
• as skin temperatures rise, radiation convection
  loses increase

• sweat glands are stimulated ?increase
  output?evaporative loss increases
• respiratory centers are stimulated?depth of
  respiration increases

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Mechanisms for Heat Gain

• Skin receptors notice that temperature is
  dropping?preoptic nucleus is notificed
• heat loss center is inhibited
• heat gain center is activated
• sympathetic vasomotor center decreases blood flow
  to dermis of skin
• vasoconstriction reduces heat loss by radiation,
  convection conduction
• blood returning from limbs is shunted into deep
  veins
• Piloerector muscles are stimulated?hair stands on
  end?traps air near the skin

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Heat Gain

• If vasoconstriction cannot restore or maintain
  core temperature?shivering thermogenesis begins
• gradual increase in muscle tone which increases
  energy consumption of skeletal muscle throughout
  the body
• increases work load of muscles elevates O2
  energy consumption?produces heat which warms deep
  vessels to which blood has been shunted by
  sympathetic vasomotor center
• can increase rate of heat generation by
• 400

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Heat Gain

• Non shivering thermogenesis
• long term mechanism for heat production
• sympathetic nervous system thyroid hormone
  produce an increase in metabolism
• Heat gain center stimulates adrenal medulla via
  sympathetic ANS?epinephrine is released?increases
  rate of glycogenolysis (break down of glycogen)
  in liver skeletal muscle?metabolic rate
  increases
• preoptic nucleus regulates production of
  TRH-thyrotropin releasing hormone by the
  hypothalamus
• TRH increases production of thyroxin by thyroid
  gland
• Thyroxin is a key hormone in control of metabolism

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