the challenge: melting these 6 ice cubes as fast as possible. how to do it? make these 6 ice cubes...
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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?
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
Modes of Heat Exchange: Conduction Convection Radiation Evaporation
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.
Negative feedback
Add coversor clothingor enter sleeping bag
Skin tempAnd Core body temp
Detected by thermoreceptors in skin
Activity in sensory nerves
Hypothalamus
Sympathetic nerves
Relax smooth muscle in cutaneous arterioles
Blood flow to skin
Heat loss by conduction & radiation
Somatic nerves Muscle tone
Heat productionSweat Glands
Sweat production
Evaporative heat loss
Core temp.
Voluntary behaviors
Remove coversTurn on fan
Heat loss
Cerebral cortex
Conductive heat loss
Radiative heat lossConvective heat loss
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)
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?
Add covers Conductive heat loss
Radiative heat loss
Skin tempAnd Core body temp
Detected by thermoreceptors in skin
Activity in sensory nerves
Hypothalamus
Sympathetic nerves
Relax smooth muscle in cutaneous arterioles
Blood flow to skin
Heat loss by conduction & radiation Core temp.
Somatic nerves Muscle tone
Heat productionSweat Glands
Sweat production
Evaporative heat loss
Cerebral cortex
Voluntary behaviors
Remove coversTurn on fan
Heat loss
p. 595 Fig 16-19
• Explain “chills” at onset of a fever
• Explain “sweat” when a fever “breaks”
• How does Tylenol reduce a fever?
To reach new,Higher set point
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.”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.
Central &PeripheralThermoreceptorsTylenol 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.
Are negative feedback loops subject to modification?
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
minimizedResponses begin even before core temperature increases! Not just negative feedback.
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
~37o
CBe able to explain the physiology in each of these situationswith a detailed diagram of negative feedback responses!