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Announcements

Announcements. Lab this week: Frog Reflexes Review information on lab webpage Topics Thermoregulation and Glucose Homeostasis and Frog Reflexes. 1QQ # 3. Name on top edge, back side of paper Answer on blank side of paper. Answer one of the following:.

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Announcements

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  1. Announcements • Lab this week: Frog Reflexes • Review information on lab webpage • Topics • Thermoregulation and • Glucose Homeostasis and • Frog Reflexes

  2. 1QQ # 3 Name on top edge, back side of paper Answer on blank side of paper. Answer one of the following: • In a reflex or negative feedback loop, what two components are connected by an efferent pathway? • In a reflex or negative feedback loop, what two components are connected by an afferent pathway? • Name three “effectors” involved in thermoregulation.

  3. Types of Stimuli:MechanicalElectrical Chemical LightThermal

  4. Negative Feedback Loop Negative feedback Compares “actual” condition to “desired” condition (set point)

  5. Convective heat loss Conductive heat loss Skin temp Radiative heat loss 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 Central thermoreceptors Cerebral cortex A problem with this example? Somatic nerves Voluntary behaviors Remove coversTurn on fan, etc via Somatic nerves Skeletal Muscles

  6. More on Body Temperature p. 583-588 • Acute thermoregulation by nervous system • Long-term thermoregulation by hormones • Thyroid Hormones and Basal Metabolic Rate • Epinephrine ( = adrenalin) • Factors affecting BMR Table 16-5 p. 584 • What is the physiology behind the recommendation that a person camping in cold environment eat a warm meal and immediately get into their sleeping bag?

  7. 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

  8. Negative feedback loops can be modified by repeated experience. • 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, this is Feed Forward (requires experience). FF is evidence of Acclimitization. Acclimitization ≠ Adaptation

  9. 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 Analogy: Experience driving a car… approaching a curve

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

  11. Positive feedback • Inherently unstable • Examples of Positive Feedback in Physiology • Heat stroke • 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) Homeostasis is achieved by negative feedback loops: the integrator detects deviations from set point and orchestrates responses produced by effectors that return the parameter toward the set point.

  12. 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?

  13. ~37oC Be able to explain the physiology in each of these situationswith a detailed diagram of negative feedback responses and the modes of heat exchange involved.

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