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

Windchill

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 lossCore temp.

Voluntary behaviors

Remove coversTurn on fan

Heat loss

Cerebral cortex

Conductive heat lossRadiative heat loss

Convective 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 lossRadiative 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!

Positive feedback • Inherently unstable• Examples of Positive Feedback in Physiology

– Heat stroke (diagrammed on next slide)– formation of blood clot– menstrual cycling of female sex hormone

concentrations– generation of action potentials in nerve fibers– uterine contractions during childbirth

• Each of these examples terminate naturally (self limiting)

Increasecell

metabolism

Increase Body Temp.

Failure of 1. Brain function &

2. Heat loss mechanisms

Sympathetic outflow

Blood Pressure

Blood Flow to brain

Disrupted functionof neurons

Cutaneous vasodilation

Heat Stroke

Sweating

So far… Humans (endotherms)

• Endotherms adjust heat exchange and metabolism by processes of negative feedback to achieve homeostasis of core body temperature.

• What about ectotherms?

http://z.about.com/d/gonyc/1/0/8/R/turtles.jpg

Lab This Week:Heat Exchange in Clay Models

and Living Reptiles inFive Simultaneous Experiments

1) Overview & instructions2) Set up conduct experiments, gather data, create graph and prepare oral report.3) Communicate results to class