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 covers or clothing or 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 nervesMuscle tone Heat production Sweat Glands Sweat production Evaporative heat loss Core temp. Voluntary behaviors Remove covers Turn on fan Heat loss Cerebral cortex Conductive heat loss Radiative 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 coversConductive 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 & radiationCore temp. Somatic nervesMuscle tone Heat production Sweat Glands Sweat production Evaporative heat loss Cerebral cortex Voluntary behaviors Remove covers Turn on fan Heat loss

p. 595 Fig 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 & Peripheral Thermoreceptors 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.

Are negative feedback loops subject to modification?

Acclimatization 1 st day on the job –Increase body temp….. Delayed sweating via negative feedback 10 th 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.

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

~37 o C Be able to explain the physiology in each of these situations with a detailed diagram of negative feedback responses!