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

2. Name three “effectors” involved in thermoregulation.
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: Mechanical Electrical
Chemical
Light Thermal

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

5. A problem with this example?
Add covers or clothing or enter sleeping bag
Conductive heat loss
Radiative heat loss
Convective heat loss
Skin temp
And Core body temp
Detected by thermoreceptors in skin
Central thermoreceptors
Activity in sensory nerves
Cerebral cortex
A problem with this example?
Somatic nerves
Hypothalamus
Voluntary behaviors
Sympathetic nerves
Relax smooth muscle in cutaneous arterioles
Remove covers Turn on fan, etc via
Somatic nerves
Muscle tone
Skeletal Muscles
Sweat Glands
Sweat production
Evaporative heat loss
Heat production
Heat loss
Blood flow to skin
Core temp.
Heat loss by conduction & radiation

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. p. 595 Fig 16-19 Explain “chills” at onset of a fever
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?
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.
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. Heat Stroke Blood Pressure Blood Flow to brain Cutaneous vasodilation
Sympathetic outflow
Blood Pressure
Blood Flow to brain
Disrupted function of neurons
Cutaneous vasodilation
Sweating

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 situations with a detailed diagram of negative feedback responses and
the modes of heat exchange involved.