Controlling the Internal
Environment I - Regulation of
Body Temperature
Keywords (reading p. 865-873)
• Temperature effects
– On reactions
– On lipid bilayer
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Endotherm
Ectotherm
Homeostasis
Thermoregulation
Behavioral
thermoregulation
• Physiological
thermoregulation
– Countercurrent heat
exchange
– Shivering
– Effect of large size
– insulation
Temperature
• Affects the rates of reactions and the
characteristics of macromolecules
• Since organisms are machines made of
macromolecules in which chemical
reactions occur, temperature is an very
important environmental feature
Temperature affects the rates of
reactions, e.g. enzyme catalyzed
reaction
Illustrated by gas molecules in a
balloon slowing down if they are
cooled
What is the magnitude of
temperature effects for
physiological processes or
biochemical reactions?
• Increase by 2-3 fold for a 10°C increase in
temperature.
• Q10 value = 2 to 3
Q10 values differ for different
physiological processes or
biochemical reactions
• Some will speed up more, some less
• This can ruin coordination of enzymes and
reactions in metabolism, e.g., mitochondria
Temperature affects
characteristics of
macromolecules
• Example: lipid bilayer
Lipid bilayer
Structure of an unsaturated
phospholipid
Bilayer with unsaturated
phospholipid stays fluid at lower
temperatures
Since temperature has such a
fundamental influence on
biochemistry and physiology,
animals:
• A. regulate their body temperatures so they
aren’t affected by temperature or can live
under a wide range of conditions
• B. Don’t regulate their temperature and
accept metabolic consequences or live
under small range of conditions
Endotherms vs. Ectotherms
• Ectotherms have a body temperature the
same as their environment
• Endotherms use heat from metabolism
– When endotherms are able to regulate their
temperature they are called homeotherms
Example of
endotherm
and
ectotherm
Homeostasis
• The steady-state physiological condition of
the body
• Internal fluctuations are small
Thermoregulation
• Regulation of body temperature
• Can be behavioral or physiological
Behavioral thermoregulation
Example of
physiological:
countercurrent
heat exchange
• Arteries and veins in
appendages are closely
associated
• Hot arterial blood passes
heat to returning venous
blood.
• No heat is lost
Blood vessels in a bird leg
• Similar mechanism in flippers of marine
mammals
• Blood flow can be controlled so that heat is
lost. Blood goes to alternate veins close to
the surface.
Countercurrent exchange is a trick used
by many animals
Tuna heat exchanger
Great white shark
Body surface
7
5
12
10
17
15
22
20
27
25
Body core
Other tricks: shivering
• Non-shivering thermogenesis: brown fat
• Using ATP to contract muscles releasing
heat instead of movement
Brown fat
Short-circuiting the mitochondria
Insect preflight warmup
Another trick: reduce heat loss
• Large size - reduced surface area relative to
volume prevents heat from escaping
• Insulation - e.g., fur, feathers
• Big problem for marine mammals since
they have high body temp. and water
conducts heat faster than air
Insulating fat (blubber)