Chp 9 Thermal relations

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Chp 9Thermal relations
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Importance of Temperature

• Temperature is a major factor affecting live of
  individuals.
• The ambient temperature is important in
  determining the animal metabolic rate ? the rate
  of food acquisition
• The animals tissue temperature affects the
  biophysical processes, the efficiency of protein
  function, the viscosity of the cell fluids.

• Definitions
• Ectotherms animal temperature is dictated by
  environmental temperature ? poikilotherms because
  their temperature varies
• Endotherms animals that regulate their tissue
  tissue temperature
• Homeotherms use endogenous heat to
  thermoregulate
• Heterothermy difference in thermal realtions ?
  temporal if difference in time (ex hibernation)
  or regional (body parts)

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• Can you give examples for each cases?

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Temperature and Heat

• Temperature measure of the intensity of
  molecular movement within an object.
• Heat a form of energy due to the motion of the
  atoms forming the object. The amount of heat
  depends on the size of the object as well as its
  temperature

• Heat moves by conduction or convection from high
  to low temperatures
• The transfer of heat raises the temperature of
  the object receiving heat and vice versa
• Thermal equilibrium temperatures are the same

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Heat transfer between animals and their
environment

• Conduction transfer of heat through
  atomic-molecular interactions ?by direct contact
• Convection heat transferred through macroscopic
  motion? flow wind

• Radiation all objects emit electromagnetic
  radiations which reflects against surface and
  warm them.
• Evaporation the transformation of water from
  liquid to gas use energy ? loss of heat due to
  vaporization

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Heat gain and loss in nature

• Radiant temperature of the sky
• The sky temperature is cooler than the earth and
  animals ? loss of energy from earth ? sky

• Solar radiation
• High and visible in the color spectrum ? heat
  gained by earth and animals

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• Desert hare Why such large ears?

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Poikilothermy - Ectothermy

• Most common all invertebrates and many
  vertebrates ? animals body temperature varies
  with the environment.
• Terrestrial animals have the possibility to
  adjust their body temperature with behavior
  pattern (basking in the sun, resting
  underground..) ? behavior thermoregulation if
  body temperature is fairly constant
• Eurythermal can function over a wide range of
  temp
• Stenothermal function in a narrow range of
  temperature

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Physiological responses in poikilotherms

• Acute response rapid changes in metabolic rate ?
  follows an exponential function of body
  temperature
• Factor by which the MR increase when body
  temperature increase by 10 temperature
  coefficient Q10
• Q10 Rt/R(t-10)
• Around 2-3 for poikilotherms

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Physiological responses in poikilotherms

• Chronic response Exposure to different
  temperature will induce different metabolic
  response ? acclimation
• Initial response is a drop in metabolism
• Followed by an increase ? compensation
• Acclimation is due to a change in the number and
  activities of enzymes involved in metabolism.

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Effects of temperature at the biochemical levels

• Enzymes work faster at higher temperatures
• Lipids are more fluid at higher temperatures

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Homeothermy in Mammals and Birds

• Core body temperature fairly constant
• Require regulation ? brain involvement
• Basal metabolic rate in these species is the
  metabolism rate when the animal is resting,
  fasting and at thermoneutral zone (TNZ)
• Metabolic rate increases in both cold and hot
  environments
• Why?

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Thermoneutrality

• Varies with species
• Some mouse species have a TNZ of 30-35oC
• Eskimo dogs - 25oC to 30oC

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Thermoregulation
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How does Fever relate to thermoregulation?

• http//physio1.utmem.edu/blatteisc/index.php

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Thermoregulation basis

• Often, the external temperatures are lower than
  the animals core body temp ? animal needs to
  energy to increase body temp
• The rate of loss varies with the animals M
  C(TB-TA )
• C characterizes the animals ability to loose
  heat
• If I1/C, I insulation measure an animal
  overall resistance to loose heat

• Main factors affecting I
• Fur
• Posture
• others

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Temperatures below thermoneutrality

• A) the cooler the temperature, the higher the
  metabolic rate
• B) however, near the TNZ the metabolism does not
  fall to 0 but reach BMR
• The slope of the line is directly related to the
  level of insulation present in the animal

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Insulation

• Pelage pilomotor response
• Plumage pilomotor response
• Blood flow vasoconstriction/dilation
• Posture

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Heat production

• Metabolism
• Shivering
• Non shivering thermogenesis ? brown adipose
  tissue brown fat

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Mammals and birds in hot environments

• Behavorial defenses
• Insulation
• Body reactions such as panting, increased
  breathing rate
• Regional heterothermy
• Countercurrent exchange
• Evaporation costly ? loss of water ultimate
  line of defense

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Heat loss

• Three active mechanisms
• Sweating common in human ? loss of water and
  salts in plasma, absent in some species such as
  rodents, rabbits
• Panting in birds, some mammals such as dogs
• Gular fluttering in birds

• Consequences Animals adapt to changing
  temperatures, especially winter/summer?
  acclimatization
• Evolutionary changes

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Hibernation Estivation Daily torpor

• A mean to escape the demands of homeothermy
• Torpor
• Controlled hypothermia
• Body temperature fall to close approximate
  ambient temperatures
• During winter ? hibernation
• During summer ? estivation
• During certain part of the day ? daily torpor

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Hypothermia

• Most likely the animal turn down its metabolism ?
  cooling
• Animals control their arousal
• Animals arouse from hypothermia once in a while
  during the hibernation
• Animals able to thermoregulate if the
  temperatures fall to levels too low
• Animals need to prepare for hibernation by
  storing fat
• Several mammal groups use hibernation to survive
  winter
• Rare in birds

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Controlled hypothermia

• Some species allow their temperature to decrease
  but not to ambient temperature
• Chickadees temperature decrease by 7oC
• Bears temperatures reach31-33oC

• What are the advantages of such process?
• Compared to no hypothermia
• Compared to full hypothermia

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Warm-bodied fishes

• Most fishes are poilokilotherm. However, larger
  predator fishes such as some sharks and tunas
  have muscles which have a higher temperature than
  the body
• They need to swim vigorously in order to catch
  fast preys
• They have
• A higher metabolic rate in these muscles ? heat
  production
• However, in order not to loose it through blood
  circulation ? presence of a counter-current
  mechanism.

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Endothermy in Insects

• At rest, not enough heat is produced to warm up
  the insect
• Heat is produced by muscles during flight
• Temporal and spatial heterothermy
• Endothermy when active only and in the thorax
  muscles
• Ex sphinx moth, bumble bee (the flight muscles
  can be used for shivering)

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Endothermy in insects

• The higher the temperature, the more efficient
  the flying ? the more energy and heat produced
• They thermoregulate by controlling blood
  circulation from thorax to abdomen, by varying
  the degree of body insulation and by controlling
  muscle activity
• Ex Bumble bee warm themselves before being able
  to fly (sun exposure and shivering). Then,
  flight can maintain the warmth

• Whats a mosquito to do in order to fly?
• It has a large body surface and very low weight
  (muscles).
• It cannot produce much heat and loose it fast