The Challenge: Melting these 6 ice cubes as fast as possible. How to do it?

1. 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?

2. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

3. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

4. Windchill

5. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

6. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

7. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

8. Modes of Heat Exchange: Conduction Convection Radiation Evaporation

9. 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.

10. Negative feedback

11. Convective heat loss Conductive heat loss Skin temp Radiative heat loss Cerebral cortex Detected by thermoreceptors in skin Hypothalamus Heat loss Sympathetic nerves Sweat Glands Muscle tone Heat production Relax smooth muscle in cutaneous arterioles Activity in sensory nerves Blood flow to skin Sweat production Evaporative heat loss And Core body temp Heat loss by conduction & radiation Core temp. Add coversor clothingor enter sleeping bag Voluntary behaviors Remove coversTurn on fan Somatic nerves

12. 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)

13. 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?

14. Conductive heat loss Skin temp Radiative heat loss Heat loss Muscle tone Heat production Activity in sensory nerves Evaporative heat loss Sweat production Blood flow to skin And Core body temp Heat loss by conduction & radiation Core temp. 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

15. Central &PeripheralThermoreceptors 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

16. Are negative feedback loops subject to modification?

17. 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.

18. 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

19. ~37oC Be able to explain the physiology in each of these situationswith a detailed diagram of negative feedback responses!

20. 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)

21. Blood Pressure Blood Flow to brain Cutaneous vasodilation Disrupted functionof neurons Sympathetic outflow Sweating Heat Stroke

22. 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?

25. Lab This Week:Heat Exchange in Clay Models and Living Reptiles inFive Simultaneous Experiments 1) Overview & instructions 2) Set up conduct experiments, gather data, create graph and prepare oral report.3) Communicate results to class