Controlling the Internal Environment I - Regulation of Body Temperature

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Controlling the Internal Environment I -
Regulation of Body Temperature
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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

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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

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Temperature affects the rates of reactions, e.g.
enzyme catalyzed reaction
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Illustrated by gas molecules in a balloon slowing
down if they are cooled
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What is the magnitude of temperature effects for
physiological processes or biochemical reactions?

• Increase by 2-3 fold for a 10C increase in
  temperature.
• Q10 value 2 to 3

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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

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Temperature affects characteristics of
macromolecules

• Example lipid bilayer

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Lipid bilayer
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Structure of an unsaturated phospholipid
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Bilayer with unsaturated phospholipid stays fluid
at lower temperatures
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Maintaining membrane fluidity at different
temperatures
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Melting temperatures of some saturated fatty acids
Name symbol melting T (C) Lauric 120 44.2 M
yristic 140 53.9 Stearic 200 69.6
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Melting temperature of some unsaturated fatty
acids
Name symbol melting T Palmitoleic 161 -0.5 Ol
eic 181 13.4 Linoleic 182 -5.0 Linolenic 183
-11.0
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Fatty acid composition of membranes from animals
acclimated to different temperatures
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Ratio of saturated to unsaturated
saturated/unsaturated Class arctic
sculpin rat 0C 37C Choline 0.59 1.22
Ethanolamine 0.26 0.65 Serine/inositol 0.48
0.64
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Ratio of saturated to unsaturated
Class goldfish goldfish 5C 25C Cholin
e 0.66 0.82 Ethanolamine 0.34 0.51 Serine/in
ositol 0.46 0.63
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Regulation of desaturase activity

• Desaturase is a membrane associated protein
• Under high temperature conditions, high fatty
  acid saturation
• Under low temperature, increased unsaturation

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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

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Lipid protein interactionsExample The chemical
characteristics of milk
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Curdling of milk
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The making of whipped cream and butter
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Since temperature has such a fundamental
influence on biochemistry and physiology, animals

• A. regulate their body temperatures so they
  arent affected by temperature or can live under
  a wide range of conditions
• B. Dont regulate their temperature and accept
  metabolic consequences or live under small range
  of conditions

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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

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Example of endotherm and ectotherm
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Homeostasis

• The steady-state physiological condition of the
  body
• Internal fluctuations are small

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Thermoregulation

• Regulation of body temperature
• Can be behavioral or physiological

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Behavioral thermoregulation
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Brandt's Cormorants, Phalacrocorax penicillatus,
taking advantage of coastal morning sunlight.
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Effects of 3,4-methylenedioxymethamphetamine and
related amphetamines on autonomic and behavioral
thermoregulation byJaehne EJ, Salem A, Irvine
RJ.Department of Clinical and Experimental
Pharmacology,University of Adelaide, Adelaide,
South Australia, 5005, Australia. Pharmacol
Biochem Behav. 2005 May 16 ABSTRACT 3,4-Methylen
edioxymethamphetamine (MDMA, 'ecstasy') and
related amphetamines such as para-methoxyamphetami
ne (PMA) disrupt normal thermoregulation in
humans and rats. Behavior, an important component
of thermoregulation in mammals, has not been
investigated with respect to these drugs. This is
surprising as harm minimization depends on
appropriate thermoregulatory behavior by drug
users. The effects of MDMA (10 mg/kg), PMA (10
mg/kg) and d-amphetamine (2 mg/kg) were therefore
studied in Sprague-Dawley rats, with telemetry
implants measuring core body temperature (T(C)),
locomotor activity and heart rate. Rats were
administered an amphetamine or saline and
confined to an ambient temperature of 21, 30 or
15 degrees C for 30 min, before being able to
choose their preferred temperature (T(P)) on a
thermally graded runway (11-41 degrees C).
Confinement at 21 degrees C had little effect on
T(C) in any group. At 30 degrees C MDMA and PMA
increased T(C) compared to saline (plt0.001). MDMA
treated animals behaviorally overcompensated for
this effect (plt0.01). Locomotor activity after
MDMA treatment was significantly elevated
compared with saline (plt0.01). In contrast, at 15
degrees C MDMA administration resulted in a lower
T(C) than saline (plt0.001). MDMA and PMA disrupt
autonomic components of thermoregulation, while
behavioral components are disrupted to a lesser
extent. These results highlight differences in
thermoregulatory responses to individual drugs,
which were only evident when behavior was
measured, and this may be important in assessing
their risk.
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Example of physiological countercurrent heat
exchange
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• Arteries and veins in appendages are closely
  associated
• Hot arterial blood passes heat to returning
  venous blood.
• No heat is lost

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Blood vessels in a bird leg
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• Similar mechanism in flippers of marine mammals

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• Blood flow can be controlled so that heat is
  lost. Blood goes to alternate veins close to the
  surface.

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Countercurrent exchange is a trick used by many
animals
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Tuna heat exchanger
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Great white shark
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Body surface
5 10 15 20 25
7 12 17 22 27
Body core
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Other tricks shivering

• Non-shivering thermogenesis brown fat
• Using ATP to contract muscles releasing heat
  instead of movement

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Brown fat-short circuited mitochondria
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5 in human infants
Brown fat
White fat
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Insect preflight warmup
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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

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Insulating fat (blubber)