The Challenge:

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The Challenge Melting these 6 ice cubes as fast
as possible. How to do it? Make these 6 ice
cubes last as long as possible? How to do it?
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Windchill
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Modes of Heat Exchange Conduction
Convection Radiation Evaporation
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Endotherms and Ectotherms

• Endotherms regulate core body temperature near a
  set point.
• Ectotherms do not achieve a constant body
  temperature body temp approximates the
  temperature of the environment.

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(No Transcript)
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Add coversor clothingor enter sleeping bag
Voluntary behaviors
Remove coversTurn on fan
Somatic nerves
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Negative feedback loops What to look for

• The stimulus (temperature, etc.)
• Sensors (thermo-, chemo-, photo-, mechano-
  receptors
• Afferent pathways to integrator (may not exist)
• Integrators (typically neurons or endocrine
  cells)
• Efferent pathways from integrator
• nerves
• hormones
• Effector cells or organs
• virtually any cell
• especially glands and muscles
• The response (opposes stimulus)

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Thermoregulation in a comatose patient?

In steady state Heat gain Heat loss
What if room temperature was increased or
decreased? What if additional covers were added
to the patient?
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Add covers
Cerebral cortex
Detected by thermoreceptors in skin
Voluntary behaviors
Remove coversTurn on fan
Hypothalamus
Sympathetic nerves
Somatic nerves
Sweat Glands
Relax smooth muscle in cutaneous arterioles
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p. 595 Fig 16-19
If setpoint is reset to a higher temperature,
then actual temperature is LESS THAN the new set
point, so one feels cold and adds clothing,
curls up, and shivers. These are Chills.

• Explain chills at onset of a fever
• Explain sweat when a fever breaks
• How does Tylenol reduce a fever?

Tylenol and other non-steroidal anti-inflammatory
drugs (NSAIDS) suppress the production of
eicosanoids (IL-1, IL-6, etc) so effect of these
on the set point in hypothalamus is minimized.
If setpoint is reset to a lower temperature or
back to normal, then actual temperature is
GREATER THAN the new lower set point, so one
feels hot and removes clothing, fans, and
sweats. These are the sweats when a fever
breaks.
To reach new, Higher set point
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Are negative feedback loops subject to
modification?
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Acclimatization

• 1st day on the job
• Increase body temp.. Delayed sweating via
  negative feedback
• 10th day on the job
• Sweating precedes changes in core body
  temperature
• and sweating is increased
• And salt loss in sweat is minimized

Responses begin even before core temperature
increases! Not just negative feedback.
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Acclimatization Feedforward

• Deviations from set point are minimized
• Learned (by experience)
• Anticipates changes of a physiological parameter
• Response begins before there is a change in the
  physiological variable
• Minimizes fluctuations

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37oC
Be able to explain the physiology in each of
these situationswith a detailed diagram of
negative feedback responses!