Homeostasis: Maintaining Body Temperature

Key Definitions:

  • Ectotherm: regulates body temp. via external sources e.g. the sun
  • Endotherm: can generate heat internally to regulate body temp.  e.g. metabolism in the liver.
  • Negative feedback: brings a reversal of any change of conditions back to the optimal conditions.




• Need less food as less is used in respiration, so can go for long periods of time without food and more energy obtained from food can be used for growth.


• At greater risk of predation as less active in cool environments and may need to warm up in the mornings before they can become active.
• May be incapable of activity in winter months so need to build up large energy store so can survive without eating.
Ectotherms change their behaviour or physiology to react to environmental temperature changes:
• Expose body to sun to enable more heat to be absorbed
• Orientate body towards sun so larger S.A for heat absorption (or away from sun so less heat absorbed)
• Hide in burrow reducing heat absorption
• Alter body shape to expose smaller/greater S.A to sun
• Increase rate of breathing so more water evaporates
welcome and be happy
• Fairly constant body temp. despite any external temp. changes
•  Can be active when it’s cold i.e. night/morning/winter and so can live in colder parts of the planet


• Large proportion of food intake used to maintain body temp, so more food is needed, and less food is used for growth.

Physiological adaptations:

• Water can evaporate from lungs/nose/mouth or from the skin when the sweat glands produce sweat
• Hairs on skin can be raised/lowered to trap greater/smaller insulating air layer
• Vasodilation/vasoconstriction in arterioles leading to skin to increase/decrease radiation of heat at skin surface
• Liver cells can alter their rate of metabolism
• Skeletal muscles can contract spontaneously ti generate heat via respiration in muscle cells (shivering)

Behavioural adaptations:

• Move into shade/hide in burrow
• Orientate body towards/away from the sun

 Remain inactive and spread out limbs to increase S.A, or roll into a ball to decrease S.A


Body temperature in endotherms is controlled by negative feedback:


The body also contains peripheral temperature receptors located at the extremities so there is a quicker reaction to external temp. changes as core body temperature may take some time to decrease enough for the hyperthalomous to detect a significant change.


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