HOMEOSTASIS &
TEMPERATURE REGULATION
Importance of Constant Internal
Environment
• HOMEOSTASIS is defined as:
the maintenance by an organism of a constant
internal state, regardless of external
environmental change
• This is essential so that an organism’s systems can
function efficiently
• TWO STEPS are essential in achieving homeostasis:
1. DETECT the change
2. COUNTERACT the change
Variables which are kept
constant
• Temperature
• pH
• Concentration of reactants
• Water & salt concentration
• Toxins
Two Stages of Homeostasis
• DETECTING CHANGE
• COUNTERACTING CHANGE
Role of the Nervous System
Indicate on this diagram where FEEDBACK takes place in the STIMULUS-RESPONSE pathway.
Thermoregulation in Humans
Annotate the diagram to show how temperature is regulated in humans
Feedback Mechanisms
• http://www.johnwiley.net.au/highered/interacti
ons/media/Foundations/content/Foundations/h
omeo2c/bot.htm
• Try this click & drag activity to test your
understanding of feedback loops
Temperatures life is found in
Life in general can be found across a BROAD range of temperatures on Earth,
while individual species can only withstand narrow limits
Hyperthermophilic Microbes
Pyrolobus fumarii grows best at 106⁰C
and can withstand
temperatures
up to 113⁰C
Terrestrial Thermophiles
Cataglyphis bicolor - A heat tolerant
insect in Sahara that can
maintain a core body
temperature of 56⁰C
Hypothermophilic Organisms
Algae, bacteria and lichen found at
environments from
-17⁰C to 20⁰C
Arctic Fox can survive in
temperatures as cold as -70⁰C;
uses countercurrent
exchange to
assist this.
Endotherms & Ectotherms
ENDOTHERMS
endo- meaning ‘within’
So, an animal which ….
ECTOTHERMS
ecto- meaning ‘outside’
So, an animal which….
Classes of vertebrates
which are endotherms are:
Classes of vertebrates
which are ectotherms are:
Adaptations for temperature regulation
BEHAVIOIURAL
STRUCTURAL
PHYSIOLOGICAL
Organism will alter its
body position in order to
increase or decrease its
exposure to the ambient
temperature….
Physical characteristics of
an organism which assist
with temperature
regulation- how the animal
is built….
Inner body functions of an
organism which contribute
to the response which
allows for temperature
regulation ….
Eg.
Eg.
Eg.
Australian Examplesendotherms
RED KANGAROO
• fur
• shivering
• sun basking
• seek shelter from the sun
• lick their forelimbs
• rely heavily on panting
• tail pulled into the shade of the body
Australian Examplesectotherms
BLUE TONGUE LIZARD
• During the early morning locates itself in small depressions in the open or
on tree trunks
• basking in the sun with its body as perpendicular as possible to the sun's
rays
• Throughout the day seeks cooler shadier
microhabitats.
• Inactive in burrows on cold
days.
Consider….
• What temperature is the blood of a lizard,
such as the Blue-tongue when it is active?
• What happens to a lizard’s blood temperature
when the environment cools down?
• Does an active lizard have warm or cold
blood?
• WHY IS IT MISLEADING TO REFER TO
ECTOTHERMS AS COLD BLOODED?
Hibernation
Example: An echidna enters state of TORPOR during winter months
when the average ambient temperature remains about 5⁰C
- Torpor is a state of inactivity, when an animal is ‘sluggish’
- Echidnas enter a state of torpor every 22 days or so.
- Body temperature goes down to 9⁰C
- Return briefly to a body temperature of 30⁰C for about 3 days
before returning to torpor.
Would this adaptation be described as behavioural or physiological?
What is the advantage in terms of thermoregulation for this
adaptation?
Advantages of Endothermy
Advantages of Ectothermy