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1
Controlling the Internal
Environment I - Regulation of
Body Temperature
Keywords (reading p. 925-930)
• Temperature effects
– On reactions
– On lipid bilayer
• 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
http://www.youtube.com/watch?v=ZgTTUuJZAFs
http://www.youtube.com/watch?v=ZvrJgGhnmJo
Frozen tree frog
• http://www.youtube.com/watch?v=Fjr3A_k
fspM
2
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 bilayerhttp://www.youtube.com/watch?v=ULR79TiUj80&feature=related
http://www.youtube.com/watch?v=mbcWGU8fpxA
http://www.youtube.com/watch?v=0ekfkxwl5bQ
Structure of an unsaturated
phospholipid
3
Bilayer with unsaturated
phospholipid stays fluid at lower
temperatures
Maintaining membrane fluidity at
different temperatures
Melting temperatures of some
saturated fatty acids
Name symbol melting T (°C)
Lauric 12:0 44.2
Myristic 14:0 53.9
Stearic 20:0 69.6
Melting temperature of some
unsaturated fatty acids
Name symbol melting T
Palmitoleic 16:1 -0.5
Oleic 18:1 13.4
Linoleic 18:2 -5.0
Linolenic 18:3 -11.0
Fatty acid composition of
membranes from animals
acclimated to different
temperatures
Ratio of saturated to unsaturated
saturated/unsaturated
Class arctic sculpin rat
0°C 37°C
Choline 0.59 1.22
Ethanolamine 0.26 0.65
Serine/inositol 0.48 0.64
4
Ratio of saturated to unsaturated
Class goldfish goldfish
5°C 25°C
Choline 0.66 0.82
Ethanolamine 0.34 0.51
Serine/inositol 0.46 0.63
Regulation of desaturase activity
• Desaturase is a membrane associated
protein
• Under high temperature conditions, high
fatty acid saturation
• Under low temperature, increased
unsaturation
Desaturase in Tetrahymena
• Phospholipids are constantly cycled into the
lipid bilayer.
• Exposed desaturase will form unsaturated
PLs that will then go into bilayer increasing
fluidity
The making of whipped cream and
butter
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
5
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 Brandt's Cormorants, Phalacrocorax
penicillatus, taking advantage of
coastal morning sunlight.
6
Example of
physiological:
countercurrent
heat exchange
http://www.youtube.com/wat
ch?v=TMCf7SNUb-Q
• 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
7
Tuna heat exchanger
Great white shark
5
10
15
20
25
7
12
17
22
27
Body surface
Body core
Other tricks: shivering
• Non-shivering thermogenesis: brown fat
• Using ATP to contract muscles releasing
heat instead of movement
Brown fat-short circuited
mitochondria 5% in human infants
Brown fat White fat
8
Insect preflight warmup
http://www.youtube.com/watch?v=_WP2XwBhmAk
http://www.youtube.com/watch?v=BQ5bEdTZgds&feature=related
http://www.youtube.com/watch?v=QsYFpIYaty4
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)
• thermal camera shows how difficult it is to
be a little seal in the Antarctic. The larger
red image is the mother seal who is
followed by her little blue pup. Blue
represents cold temperatures; red and
orange are warm areas. Mom with her thick
blubber layer appears much warmer than
her new born pup.