Thermoregulation
Maintaining a stable body
temperature
• Why do organisms need to maintain a stable
body temperature??
Optimum Temperatures
• Organisms must keep their body temperature
between a specific range in order to survive.
• Enzyme activity
• Metabolic processes
Body Temperature in animals
• There are two types of organisms that maintain
their body temperature in very different ways
• Ectothermic organisms
• Endothermic organisms
• What do these terms mean? Can you give some
examples of each?
Ecto (outside); therm (heat)
• Use external environment to maintain body
temperature.
• Produce little heat
• Lose heat quickly
• Use less energy
• Become very inactive when it gets cold
• Fish, Reptiles, Insects
Endo (inside); therm (heat)
• Maintain relatively constant body
temperature
• Generate a lot of heat from within via internal
heat production
• Generally have insulating structure to reduce
heat loss (e.g. feathers, fur, fat)
• Also develop behavioural and physiological
adaptations to prevent heat loss
Endo (inside); therm (heat)
• Mammals and birds
• Homeothermic: organisms that can maintain a
stable body temperature (e.g. mammals)
• Poikilothermic: organisms whose body
temperature varies considerably due to its
surroundings (e.g. reptiles and insects)
Heat Transfer
• Heat is a question of balance
• Too HOT and animals must
find ways to lose heat
• Too COLD and animals must
find ways to gain heat
Heat Transfer
• To understand why animals do the things they
do you must understand how heat can be
transferred.
QUESTION
• What are the ways in which heat can be
transferred?? How can animals lose or gain
heat??
Heat Transfer
• Conduction: transfer of heat from a hotter
object to a cooler object via contact.
• Radiation: transfer of heat from a hotter
object to cooler object via infra-red waves.
Heat Transfer
• Convection: Transfer of heat by warm air, or
water, rising and being replaced by cooler air
or water.
• Evaporation: The process of changing a liquid
into a gas. The heat from the body can
evaporate water and cause a cooling effect.
Heat Transfer
Heat transfer RAP!!!!
Heat Gain and Loss
• Gain
– Basic metabolic processes
– Shivering
– Exercise or other muscular activity
– Radiation and conduction to the body
• Loss
– Evaporation sweat
– Panting
– Convection
– Radiation and conduction from the body
Heat Loss and Gain
VIDEO!!!!!
Systems Involved
• Thermoregulation occurs via nerves and
hormones
• It involves many sensory inputs and several
effector responses that act together to
maintain a stable temperature
Linking to other systems
• Thermoregulation is strongly related to the
Nervous system and the Endocrine system
Worksheet
Investigating Sweating
What you need to know:
 How does sweating affect body
temperature?
 Why does sweating affect body
temperature?
 How can models help us investigate
how the body works?
Question:
 How does water evaporate?
For water to evaporate, it must absorb
heat from its surroundings
Dry towelling
cloth
Cotton
wool
 Set up the equipment as shown opposite
 Fill the conical flask with hot water from the
kettle
 Record the temperature and start your stop
clock
 Record the temperature every minute for 10
minutes. Record your data in a suitable table
Time
(mins)
 Repeat with a wet towelling cloth
0
(START)
1
Temperature (°C)
Dry Flask
Wet Flask
To Do:
 Plot a graph of your data
 Which flask cooled faster?
 How do you explain your results?
 Was your experiment a fair test – if not,
why not?
How could you make this experiment more of
a fair test?
Systems Involved
• Brain – Hypothalamus
• Lowering or raising the temperature of the
hypothalamus initiates regulatory responses
• Changes occur in heat production and heat
exchange
• Temperature cells act
as misalignment
detectors
Core body
temperature
>37°C
Thermoreceptors
Hypothalamus
nerves
Muscles
reduce
activity
Sweat
glands
increase
secretion
Muscles of
skin arteriole
walls relax
Skin arteries dilate
More blood to the
skin.
More radiation &
conduction of heat
More water covers the
skin.
More evaporation
Less heat generated
Systems Involved
• Hypothalamus responds to receptors and
coordinates appropriate nerve and hormonal
responses
Systems Involved
• The hypothalamus can release hormones that
initiate the release of further hormones.
• For example as the temperature drops the
pituitary gland will be stimulated and release
a thyroid stimulating hormone
• The thyroid gland in turn produces hormones
which increase the metabolic rate therefore
increasing heat production
Systems Involved
Systems Involved
• Skin – thermoreceptors act as disturbance
detectors.
• Detect change in external environment and
triggers responses before it effects internal
body temperature.
• Responses include erector muscles of hairs
contract and hairs stand up, blood vessels
constrict.
• These are the effectors for mediating change.
Skin
Negative feedback
• Temperature regulation by the skin is part of a
negative feedback system.
• Output is fed back to receptors and becomes
part of a new stimulus response cycle.
NEGATIVE
FEEDBACK
Thermoreceptors
Core body
temperature
>37°C
Thermoreceptors
Blood
temperature
Muscles of
skin
arteriole
walls relax
nerves
Hypothalamus
Sweat
glands
increase
secretion
Muscles
reduce
activity
Body
loses
heat
Return
to 37°C
Thermoregulation
• VIDEO REVIEW
Summary
•
•
•
•
•
Ectothermic
Endothermic
Homeothermic
Poikilothermic
Heat transfer – Conduction, Convection,
Radiation & Evaporation
• Heat Gain and Loss
• Endocrine and Nervous system involved
Review Questions
• Page 256 of the text book.
- Questions 17 - 21
Adaptations and Thermoregulation
• Apart from physiological adaptations, animals
also develop behaviours and physical
structures that help them regulate their body
temperature.
Heat Loss and Gain
• Must remember the ways in which heat can
be transferred.
• These processes work on a temperature
gradient.
• Can you explain what this means?
Heat Loss and Gain
• Temperature gradient simply refers to the
difference in temperature between two
things.
• For example the lizard and the rock.
Heat Loss and Gain
Heat Loss and Gain
• The rock is warmer than the lizard so the heat
moves, via conduction, from the rock to the
lizard.
• As the lizard heats up and the gradient
decreases and eventually changes the heat
moves from lizard to rock.
Structural & Behavioural
• The transfer of heat needs to be controlled.
• What examples of structural and behavioural
adaptations can you think of?
Behavioural Responses
• Penguins huddling
• Burrowing underground
• Seeking shade
• Basking
• Fanning from honeybees
Behavioural Responses
• VIDEO
Counter current heat exchange
Counter current heat exchange
• The arteries and veins in certain areas, like the
foot of the penguin, run very close to each
other.
• The warmer blood in the arteries heats the
cooler blood in the veins.
Structural Responses
• Animals need to control exchange. This can
also be achieved through:
• Insulation: - Fur
- Feathers
- Fat
Structural Adaptations
• Feathers and fur insulate by trapping a thick
layer of warm air next to the skin.
• The layer of air has a protective insulating
affect keeping the animal warm.
Structural Adaptations
• The layer of air trapped by the otters fur helps
reduce the temperature gradient between the
otter and its surroundings.
• Therefore reducing heat loss and gain.
Structural Adaptations
• Blubber is also used as insulation.
• Thick layers of fat are very effective in
insulating animals against extremely cold
conditions.
Structural Adaptation
• Shape and size also play an important role.
• How do you think shape and size of an
animals can help?
Structural Adaptations
• A large surface area to volume ratio increases
heat loss
• A small surface area to volume ratio reduces
heat loss.
Structural Adaptations
Structural Adaptations
• So being larger and rounder in shape is
beneficial in a cold climate.
• For example whales and seals
• Being smaller is better for individuals in hot
climates.
Shutting Down
• Sometimes these adaptations are not enough.
• The external temperature can reach such a
point that the internal temperature of animals
reaches a critical level
Shutting Down
• The external temperature at which metabolic
activity begins to rise is called the lower
critical temperature
• The increase in metabolic rate means the
animal needs more energy.
• This can often be too difficult to find.
Shutting Down
• At this point animals will often go into
hibernation to conserve energy.
Shutting Down
• The upper critical temperature refers to the
point at which cooling mechanisms fail.
• The metabolic rate rises with the increase in
the external temperature. This an be very
dangerous.
Shutting Down
Summary
• Explain how behavioural adaptations help
regulate body temperature using specific
examples.
• Explain how structural adaptations help regulate
body temperature using specific examples.
• Explain how counter current heat exchange works
Adaptations
• Design your own animal (groups of 3)
• Choose an environment (extreme HOT or extreme
COLD)
• Draw and label adaptations that help it survive
• Include physiological, behavioural & structural
(physical)
• Present to the class!!!
• Give it a name (be creative)
• Think about possible adaptations for water balance.
BINGO
Thermoregulation, Osmosis, Radiation,
Convection, Freshwater Fish, Poikilothermic,
Insulation, Pituitary Gland, Ectotherm,
Hypothalamus, Conduction, Counter Current
heat exchange, Homeothermic, Marine Fish,
Endotherm, Receptors, Evaporation, Loop of
Henle, Thyroid Gland, Hibernation, Shivering,
Dilation of Blood Vessels.