Transcript Thermoregulation3

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.