Thermoregulation

• Thermoregulation


  The ability of an organism to keep its body temperature within a temperature range, even when the surrounding temperature is very different

  
• Thermoregulation


  • It is one aspect of homeostasis: a state of dynamic stability in an organism's internal conditions, maintained far from thermal equilibrium with its environment
  • If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs
  • The opposite condition, when body temperature decreases below normal levels, is known as hypothermia

  
• Thermoconforming organism


  Adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation

  
• How animals regulate body temperature

  • Ectotherms (do not regulate body temperature, rely on external energy)
  • Endotherms (rely on body mechanisms to regulate temperature)
  • Poikilotherms (animals with varying internal temperatures)
  • Homeotherms (animals that maintain a constant body temperature)

  
• Mechanisms through which the human body exchanges heat with the environment

  • Conduction
  • Convection
  • Radiation
  • Evaporation
• Ways animals conserve or dissipate heat

  • Some endothermic animals have insulation like fur, fat, feathers
  • Mammals increase muscle activity (shivering) and use fat layers to keep warm
  • Endotherms use the circulatory system for vasodilation and vasoconstriction
  • Some endotherms use adaptations like dolphin flukes and elephant ears to help cool down
  • Some ectothermic animals use behavioral changes to regulate body temperature
  • Some animals use evaporation to cool, like reptiles and bees
  • Some endotherms have countercurrent heat exchange in their circulatory system

  
• Thermoregulation and homeostasis


  Centered in the hypothalamus in the advanced animal brain
• Normal body temperature is within a narrow range and any temperature outside of this range can cause physiological damage

  
• How the human body regulates temperature

  1. Heat is generated by metabolism and basal metabolic rate

  2. If temperature is too high, the hypothalamus increases blood circulation to skin and initiates sweating

  3. If temperature is too low, the hypothalamus initiates shivering and thyroid hormone stimulates heat production

  
• Skin in thermoregulation


  • It is the boundary between external environment and internal organs
  • Heat exchange occurs at the skin
  • Skin can alter heat gain or loss through sweating, hair contraction/relaxation, and vasodilation/vasoconstriction

  
• Metabolic rate


  • The amount of energy consumed minus the amount of energy expended by the body
  • Basal metabolic rate (BMR) is the amount of daily energy expended by humans at rest
  • About 70% of daily energy expenditure comes from basic organ functions, 20% from physical activity, 10% for thermoregulation
• Effects of impaired thermoregulation

  • Heart increases rate and cardiac output
  • Circulatory system experiences intravascular volume depletion
  • Brain may experience ischemia and/or edema
  • Gastrointestinal tract vulnerable to hemorrhage and infection
  • Lungs can be impaired by sustained hyperventilation, hyperpnea, and pulmonary vasodilation
  • Acute renal failure due to intravascular volume depletion and impaired circulation
  • Liver cells suffer due to fever, ischemia, and cytokine increase
  • Electrolyte abnormalities, hypoglycemia, metabolic acidosis, respiratory alkalosis