Thermoregulation

• Homeostasis


  The maintenance of a constant internal environment in response to changes in the external environment.
• How homeostasis is achieved

  • Structural: the animal has particular physical features which help its survival in an otherwise hostile environment.
  • Functional: the metabolism of the animal is able to adjust to changes in conditions as they are detected.
  • Behavioural: the actions and interactions of the individual, either alone or with others, help it to survive in its particular environment.
• Feedback mechanisms


  The general mechanism of nervous or hormonal regulation in animals.
• Negative feedback


  When the response diminishes the original stimulus.
• Positive feedback


  When the response enhances the original stimulus.
• Feedback loop

  1. Stimulus

  2. Receptor

  3. Relay

  4. Effector

  5. Response

  6. Feedback
• Negative feedback is most common in biological systems.
• Positive feedback


  • A puppy begins to suckle her mother's nipple and a few drops of milk are released (the stimulus). This encourages the puppy and releases a hormone in the mother which further stimulates the release of milk (the response). The hungry puppy continues to suckle, stimulating more milk release until she stops.
• Hypothermia

  A potentially dangerous drop in body temperature, usually caused by prolonged exposure to cold temperatures
• Hyperthermia

  When a person's body temperature rises and remains above the normal 37°C
• Counter-current heat exchange (CCHE)


  1. Exchange oxygen from the high oxygen environment of the water around them into the low oxygen environment of their bloodstream

  2. Heat and cool their feet so that they don't freeze in the ices and snow

  3. Help cool their bodies
• Examples of CCHE

  • Fish gills
  • Arctic foxes and wolves
  • Jackrabbits
• Insulation

  • Birds use feathers, and most mammals use hair or fur, to trap a layer of air next to the skin and reduce heat transfer to the environment
  • In cold weather, birds fluff their feathers and animals raise their fur to thicken the insulating layer
• Hypothermia

  1. Cold exposure

  2. When the balance between the body's heat production and heat loss tips toward heat loss for a prolonged period
• During exposure to cold temperatures

  Up to 90% of your body heat escapes through your skin
• If cold exposure is due to being immersed in cold water

  Heat loss can occur 25 x faster than it would if exposed to the same air temperature
• Symptoms of hypothermia


  • Shivering
  • Slow, shallow breathing
  • Confusion and memory loss
  • Drowsiness or exhaustion
  • Loss of coordination, stumbling steps
  • A slow, weak pulse
  • In severe hypothermia, a person/animal may be unconscious without obvious signs of breathing or a pulse
• Shivering is actually a good sign that a person's/animal's heat regulation systems are still active
• Hyperthermia


  Exposure to a hot environment normally results in the activation of heat loss mechanisms, and body temperature is maintained at normal levels. However, prolonged exposure to a hot environment can result in heat exhaustion.
• Heat exhaustion

  Heavy sweating results in dehydration, decreased blood volume, decreased blood pressure, and increased heart rate. People with heat exhaustion usually feel weak, dizzy, and nauseated.
• Heat stroke

  Occurs when there is a breakdown of the normal negative-feedback mechanisms of temperature regulation.
• Symptoms of hyperthermia in dogs

  • Panting
  • Dehydration
  • Excessive drooling (ptyalism)
  • Increased body temperature - above 39° C
  • Seizures
  • Muscle tremors
  • Wobbly, uncoordinated or drunken gait or movement (ataxia)
  • Unconsciousness in which the dog cannot be stimulated to be awakened
  • Vomiting blood (hematemesis)
  • Death of liver cells
• Endotherm


  An animal that is dependent on or capable of the internal generation of heat
• Ectotherm


  An animal that is dependent on external sources of body heat
• Negative feedback systems are by far the most common found in the animal body
• Thermoregulation by the thermoregulatory center in the hypothalamus


  1. Receives input from thermoreceptors in the hypothalamus and skin

  2. Sends impulses to effectors to adjust body temperature
• Endotherms

  • Various ways of increasing metabolic heat production (thermogenesis) in response to cold environments:
  • Muscle contraction (shivering)
  • Non-shivering thermogenesis (raising hairs)
  • Brown fat tissue
• Circulatory mechanisms for controlling heat loss and gain

  1. Vasoconstriction (blood vessels constrict to reduce heat loss)

  2. Vasodilation (blood vessels dilate to allow heat loss)
• Animals with circulatory mechanisms for controlling heat

  • Hare
• Body structures and physiological responses that control heat exchange

  • Circulatory mechanisms
  • Evaporative mechanisms (panting, sweating, gular fluttering)
  • Insulation (fur, fat, feathers)
• Evaporative cooling

  1. Terrestrial animals lose water from skin, mouth, nose

  2. Sweat glands secrete sweat which evaporates to remove heat
• Insulation minimises heat loss to the environment
• Heat Stroke

  If the temperature of the hypothalamus becomes too high, it no longer functions properly. Sweating stops, and the skin becomes dry and flushed. The person/animal will become confused, irritable, or even comatose.