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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: 1. In a reflex or negative feedback loop, what two components are connected by an efferent pathway? 2. In a reflex or negative feedback loop, what two components are connected by an afferent pathway? 3.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 Add covers Conductive heat loss Skin temp And Core body temp or clothing Radiative heat loss or enter Convective heat loss Central sleeping thermoreceptors bag Detected by thermoreceptors in skin Cerebral cortex Activity in sensory nerves Somatic nerves Hypothalamus Sympathetic nerves Relax smooth muscle in cutaneous arterioles Blood flow to skin Somatic nerves Sweat Glands Voluntary behaviors Muscle tone Heat production Sweat production Skeletal Muscles Heat loss Evaporative heat loss Heat loss by conduction & radiation Remove covers Turn on fan, etc via Core temp. 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? If setpoint is reset to a p. 595 Fig 16-19 higher temperature, then actual temperature is LESS THAN the new set point, so • Explain “chills” at one feels “cold” and adds onset of a fever clothing, curls up, and These are “Chills.” •shivers. Explain “sweat” a isfever If when setpoint reset to a “breaks” lower temperature or back normal, then actual •toHow does temperature is GREATER Tylenol reduce a THAN the new lower set fever? 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 nonsteroidal antiinflammatory drugs (NSAIDS) suppress the production of eicosanoids (IL-1, IL-6, etc) so effect of these on the set point in hypothalamus is new, To reach minimized. 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 Increase cell metabolism Failure of 1. Brain function & 2. Heat loss mechanisms Increase Body Temp. Blood Flow to brain Cutaneous vasodilation Disrupted function of neurons Sympathetic outflow 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? o ~37 C 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.