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ACT
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Interactive
activity |
GA |
Gray's Anatomy |
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Animation |
pp |
PowerPoint
slide |
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FIG
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Figure |
term |
Define,
pronounce |
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Introduction to
homeostasis
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homeo = same; stasis = standing |
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Relative constancy of the internal fluid
environment
pp
pp |
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The
concept
was first articulated by [Frenchman] Claude Bernard in 1860s
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"I think I was the first to urge the
belief that animals have really two environments: a milieu
extérieur in which the organism is situated, and a milieu
intérieur in which the tissue elements live. The
living organism does not really exist in the milieu
extérieur (the atmosphere it breathes, salt or fresh
water if that is the element) but in the liquid milieu
intérieur formed by the circulating organic liquid which
surrounds and bathes all the tissue elements; this is the
lymph or plasma, the liquid part of the blood which, in the
higher animals, is diffused through the tissues and forms the
ensemble of the intercellular liquids and is the basis of all
local nutrition and the common factor of all elementary
exchanges. A complex organism should be looked upon as
an assemblage of simple organisms which are the anatomical
elements that live in the liquid milieu intérieur." |
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Claude
Bernard
(1813-1877)
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The
term "homeostasis"
was first used by
[American] Walter Bradford Cannonin 1920s
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"The coordinated physiological processes
which maintain most of the steady states in the organism are
so complex and so peculiar to living beings--involving, as
they may, the brain and nerves, the heart, lungs, kidneys and
spleen, all working cooperatively--that I have suggested a
special designation for these states, homeostasis. The
word does not imply something set and immobile, a
stagnation. It means a condition--a condition which may
vary, but which is relatively constant." |
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Cannon was the one who really established
homeostasis as a unifying concept of human physiology |
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Walter B. Cannon
(1871-1945)

Click to enlarge
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Fishbowl model
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Fish are like the cells of the [multicellular]
body |
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Internal environment of the fishbowl is a fluid
that must be maintained in relatively constant conditions for the
fish to survive in health
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Optimum temperature, high nutrient level,
high oxygen level, low carbon dioxide level, low
nitrogen-waste level, optimum pressure, etc. |
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Devices such as heaters/chillers, auto
feeders, aerators, filters keep conditions relatively constant |
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In the human body, physiological mechanisms keep
oxygen up and carbon dioxide down (respiratory system), nutrients
up (digestive system), wastes low (kidneys), temperature constant
(muscles, sweat, etc) |
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Fishbowl
Model
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Fishbowl |
Human body |
Function |
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Water |
Body fluid |
Internal environment |
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Glass bowl |
Skin |
Barrier (internal vs. external) |
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Fish |
Cells |
Stay alive |
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Air pump |
Lungs |
Keep O2 level constant (high) |
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Filter |
Kidneys |
Keep nitrogen wastes constant (low) |
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Heater |
Muscles |
Keep temperature constant (high) |
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Feeder |
Digestive system |
Keep nutrient levels contant (high) |
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Everything working together |
Relatively constant conditions |
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To visit Kevin's fish
Clyde click
here
For a REAL fish story click
here for a SCARY fish story click
here
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Engineered control system (thermostat) model
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Example: thermostatic heating system in a home |
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Components of an automatic control system
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Variable is the characteristic of the internal
environment that is controlled by this mechanism (internal temp in
this example) |
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Sensor (receptor) detects changes in variable and
feeds that information back to the integrator (control center)
(thermometer in this example) |
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Integrator (control center) integrates (puts
together) data from sensor and stored "setpoint" data
(thermostat in this example) |
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Setpoint is the "ideal" or
"normal" value of the variable that is previously
"set" or "stored" in memory |
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Effector is the mechanism (furnace in this example)
that has an "effect" on the variable (internal temperature
in this example) |
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Changes in temp are detected by thermometer, which
feeds info about the actual temp back to thermostat, which has been
previously set to ideal (setpoint) value; thermostat compares actual
value to setpoint value and sends signal to furnace, which fires up and
changes the internal temp back toward setpoint (furnace will shut down
when thermostat determines actual temp is now higher than setpoint temp) |
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Negative feedback
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Occurs when feedback (from sensor to integrator)
results in a reversal of the direction of change |
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In example, thermostat's response causes
temperature decrease to reverse and become a temperature increase |
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Negative feedback tends to stabilize a system,
correcting deviations from the setpoint |
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Human example: shivering in response to cooling of
body during cold weather |
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Positive feedback
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Occurs when feedback (from sensor to integrator)
results in an amplification of the change (same direction as
deviation from setpoint) |
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In example, positive feedback would occur if the
thermostat's response to a dropping temperature was to switch off
the furnace or to switch on the air conditioner (chiller) |
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Another example: audio "feedback" occurs
when amplified sound is picked up by microphone and then amplified
again then picked up and amplified again, and again, and again
--each time getting louder
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Can be stopped only if "feedback
loop" is broken |
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Human example: increased labor contractions
stimulated by oxytocin (OT) hormone
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Fetus's head moves into birth canal (vagina) at
start of labor, which causes the birth canal to stretch beyond
its setpoint amount of stretch, which is detected by sensors
(stretch receptors) in the vaginal wall and fed back to
hypothalamus of brain, which releases OT, which stimulates
stronger and more frequent uterine (womb) contractions, which
pushes the fetus, which causes more vaginal stretch, which
produces more OT, and so on --greatly amplifying and speeding up
labor contractions |
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Broken when baby is born (no more stretch,
thank goodness) |
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Click to enlarge
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Click to enlarge
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Engineered
Room Control |
Feedback
Loop |
Human
Body Thermoregulation |
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Room Temperature |
Variable
The characteristic that is controlled |
Body temperature |
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Thermometer |
Sensor
Detects the value of the variable |
Nerve receptors |
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Thermostat |
Integrator
Compares the actual value of the variable to a pre-determined
setpoint value |
Brain (hypothalamus) |
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Furnace |
Effector
Instrument that has an effect on (changes)
the variable |
Muscles (shivering) |
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Wallenda
model
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The Flying Wallendas
are a family of circus performers famous for
their high-wire acts (this model is that of a high-wire artist) |
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Karl Wallenda (former patriarch of the family acts)
made "sky walks" famous
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Single artist walking across single wire (very
high, very long --as in Busch Stadium walk)
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Click
here to see current family patriarch, Tino, doing these
daring skywalks |
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Uses negative feedback to maintain relatively
constant position on wire (setpoint is having wire walker's center of
gravity directly over wire) |
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Karl died in a skywalk in Puerto Rico when,
sadly, he
couldn't maintain a constant position over the wire
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That's how we all die: we each eventually lose
homeostatic constancy (but hopefully ours won't be shown on the
news) |
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Click image for Wallenda's website
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Elements of the
Wallenda Model
Variable: position of body
Setpoint: directly over
the wire
Sensors: nerve receptors (eyes, inner
ears, muscle stretch receptors, etc.)
Integrator: brain
Effectors: skeletal muscles
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Tino
Wallenda |
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Seven-person pyramid - famous Wallenda trick involved
multiple balances to maintain pyramid of 7 artists
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Fell in 1962 when front artist lost grip on balance
pole, all 7 lost their balance |
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Two died in accident, one permanently paralyzed
from waist down, all were injured |
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Recreated by Wallendas in late 1990s (premiering at
Detroit, then Forest Park in St. Louis's Circus Flora)
. . . and then in 2001, they achieved
a 10-person pyramid
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Click
here to see photos of how the pyramid is arranged and a video clip
of the "7" in action |
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Wallenda model illustrates these concepts of
homeostasis:
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Negative feedback maintenance of variable |
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Homeostasis is a dynamic, energy-consuming process |
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Homeostatic balance is vital to healthy survival
(you die when you lose it) |
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Balance of one homeostatic variable is often
interdependent with the balance of other variables |
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Kevin (left) with The
Flying Wallendas (Alida, Tino, Olinka) when they
all performed on the same program in
Circus Flora at Faust Park in 1987.
Click image to enlarge it |
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10 Ways to
Save Karl Wallenda |
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This Mini Lesson may be
updated or improved at any time.
Check back frequently or use the
link to the right to inform you of changes. |
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© 1988-April, 2007 Kevin
Patton
ALL rights
reserved
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