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.