Thermoregulation in Endotherms

• Endotherms (e.g. mammals and birds) maintain constant body temperature in narrow limits by both physiological and behavioural methods; unlike ectotherms, they can alter metabolic rate as part of their temperature control
• Advantages: Maintains a constant body temperature despite fluctuating environment, so activity possible regardless and inhabitance to colder parts of the planet
• Disadvantages: Significant part of energy intake used to keep warmth in colder climates so more food needed supply energy needs; less is used for growth
• Thermoregulatory control centre is in the hypothalamus at the base of the brain; its temperature receptors monitor blood temperature as it flows through the organ and core body temperature change
• Hypothalamus also receives impulses from peripheral temperature receptors in the skin; indicates if the external environment is cold or hot; warning that core body temperature may change shortly
• Hypothalamus sends nerve impulses along motor neurones to the muscles and liver to control internal heat input; nerve impulses are also sent to the skin to control heat output
• Sweating: Primary mechanism our body uses to cool us; on a hot day, we sweat, and it evaporates off our skin, cooling us; the energy to evaporate sweat (latent heat of vaporisation) is provided by our body
• Behaviour if Too Hot:

  • Move to shade or hide in a burrow
  • Orientate body to decrease surface area exposed to sun
  • In shade, spread out limbs to increase SA for heat loss by conduction and radiation
  • Remain inactive to reduce internal heat generation 
  • Humans can wear fewer clothes, eat cool salads and drink iced drinks
• Behaviour if Too Cold:

  • Move into a warmer place; bask in the sun
  • Orientate body to increase SA exposed to sun and heat gain from radiation
  • In extreme cold, reduce body surface area by rolling into a ball to reduce heat losses by radiation and conduction; humans can wrap their arms around them and huddle up
  • Move about to generate heat in muscles
  • Humans can put on more clothes (increase insulation of body surface), eat hot food or drink hot drinks
• Physiological Responses

  A) more

  B) less

  C) Relax

  D) flatten

  E) reduce

  F) more

  G) radiation

  H) convection

  I) erector

  J) erector

  K) contract

  L) raise

  M) insulating

  N) vasodilation

  O) capillaries

  P) more

  Q) vasoconstriction

  R) less

  S) less

  T) reduced

  U) less

  V) respiration

  W) increased

  X) more

  Y) spontaneous contractions

  Z) spontaneous contractions

  [) heat

  \) respire

  ]) panting

  ^) increases

  _) moist

  `) panting