thermoregulation

• ectotherms 


  can't control their body temperature internally
• ectotherms control their temperature by changing their behaviour meaning their internal temperature depends on the external temperature
• Ectotherms have a variable metabolic rate because they can't keep their internal temperature constant. They generate very little heat themselves.

  This means the activity level of ectotherms depends on the external temperature too - they're more active at higher temperatures and less active at lower temperatures.
• advantages of ectotherms

  • use less of their food in respiration
  • meaning they need to find less food and may be able to survive long periods without eating
  • a greater proportion of the energy obtained from food can be used for growth
• disadvantages of ectotherms

  • less active in cooler temperatures and may need to warm up in the morning before they can be active which puts them at greater risk of predators
  • may not be capable of activity during the winter as they never warm up sufficiently
  • they must have sufficient stores of energy to survive over the winter without eating
• thermoregulation 


  control of body temperature
• gains in heat of organism

  • waste heat from cell respiration
  • conduction from surroundings
  • convection from surroundings
  • radiation from surroundings
• losses of heat from an organism

  • evaporation of water
  • conduction to surroundings
  • radiation to surroundings
  • convection to surroundings
• endotherms 


  an organism that can regulate its own body temperature
• • in endotherms the liver is the main organ which regulates the body temperature
  • exergonic reactions take place which release heat
  • they use internal sources of heat to help maintain their body temperature
  • they can increase the rate of respiration in the liver to release heat
  • compared to ectotherms their internal temperature is less affected by the external temperature
  • they have a constantly high metabolic rate so they can keep their internal temperature constant
• advantages of endotherms

  • have a fairly constant body temperature whatever the temperature is externally
  • activity possible in cool or high temperatures
  • ability to inhabit colder parts of the planet
• disadvantages of endotherms

  • a significant part of the energy intake used to maintain body temperature in the cold
  • more food required
  • less of the energy from food is used for growth or more food us needed in order to grow
• heat is lost from the body in 4 ways:

  1. convection- air or water moving across the surface of the skin so removing the layer of war air around us
  2. conduction- losing heat by being in contact with an object
  3. radiation- heat lost from the surface of the body to cooler still around us
  4. evaporation- heat loss which occurs when water is converted to a vapour
• hypothalamus 


  maintains a constant body temperature in mammals
• thermoreceptors can be found in:

  1. hypothalamus- detect the core temperature
  2. skin- detect external temperature
• Mechanisms to increase body temperature

  1. Muscles contract in spasms which makes the body shiver so more heat is produced from increased respiration

  2. Adrenaline and thyroxine are released to increase respiration so more heat is produced which is transferred to the blood

  3. Less sweat is secreted from sweat glands so less evaporation of water so less heat is lost

  4. Vasoconstriction reduces the flow of blood through capillaries near the surface of the skin to reduce heat loss

  5. Muscles contract causing hairs to stand up on the skin which traps a layer of insulating air reducing the loss of heat from the skin
• mechanisms to decrease body temperature

  • rate oft metabolism is reduced so less heat is generated from exergonic reactions e.g respiration
  • more sweat is secreted from sweat glands and the water in the sweat evaporates from the surface of the skin and takes heat
  • vasodilation increases blood flow through the capillaries in the surface layer which means more heat is lost from the skin by radiation and the temp is lowered
  • erector pili muscles relax so the hairs lie flat meaning less air is trapped so the skin is less insulated meaning heat can be lost more easily
• Thermoreceptors send impulses along sensory neurones to the hypothalamus, which sends impulses along motor neurones to effectors (e.g. skeletal muscles, or sweat glands and erector pill muscles in the skin). The effectors respond to restore the body temperature back to normal.
• • When thermoreceptors detect body temperature is too high, they send impulses to the hypothalamus, which sends impulses to effectors.
  • Effectors respond to increase heat loss from the body (e.g. sweat glands produce sweat) and to reduce the amount of heat that's produced by the body.
  • Body temperature then returns to normal
• • When thermoreceptors detect body temperature is too low, they send impulses to the hypothalamus, which sends impulses to effectors.
  • Effectors respond to produce more heat (e.g. adrenaline and thyroxine are released to increase metabolism) and to conserve it.
  • Body temperature then returns to normal
• negative feedback mechanism activated by a rise in body temperature

  A) thermoreceptors

  B) hypothalamus

  C) effectors

  D) vasodilation

  E) sweating

  F) hairs lie flat

  G) no shivering

  H) no adrenaline and thyroxine released

  
• negative feedback mechanism activated by a fall in body temperature

  A) thermoreceptors

  B) hypothalamus

  C) effectors

  D) vasoconstriction

  E) much less sweating

  F) hairs stand upright

  G) shivering

  H) adrenaline and thyroxine released