announcements topics lab this week: frog reflexes
DESCRIPTION
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.TRANSCRIPT
Announcements
• Lab this week: Frog Reflexes– Review information on lab webpage
• Topics• Thermoregulation and • Glucose Homeostasis and • Frog Reflexes
1QQ # 3Name on top edge, back side of paperAnswer 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:MechanicalElectricalChemicalLightThermal
Negative feedback
Negative Feedback Loop
Compares “actual” condition to “desired” condition (set point)
Add coversor clothingor 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 nerves
Muscle tone
Heat productionSweat Glands
Sweat production
Evaporative heat lossCore temp.
Voluntary behaviorsRemove coversTurn on fan, etc via
Heat loss
Cerebral cortex
Conductive heat lossRadiative heat loss
Convective heat loss Central thermoreceptors
Skeletal Muscles
Somatic nerves
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
• 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 &PeripheralThermoreceptorsTylenol 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.
• 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
Negative feedback loops can be modified by repeated experience.
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
Increasecell
metabolism
Increase Body Temp.
Failure of 1. Brain function &
2. Heat loss mechanisms
Sympathetic outflow
Blood Pressure
Blood Flow to brain
Disrupted functionof neurons
Cutaneous vasodilation
Heat Stroke
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?
~37o
CBe able to explain the physiology in each of these situationswith a detailed diagram of negative feedback responses andthe modes of heat exchange involved.