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

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.

Types of Stimuli: Mechanical Electrical Chemical Light Thermal

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

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

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?

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

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

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

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

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.

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?

~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.