Connect!

How does your body react to being cold?
What
happens once you warm up?
Explain
how a thermostat and furnace work
together to keep your house temperature
within a narrow range.
Feedback Mechanisms

As mentioned previously, organisms
constantly monitor and adjust to changes
in the external and internal environments.
Often when a change is detected a
corrective action must be taken that
returns the organism’s systems to normal.
These actions are called feedback
mechanisms.

a feedback mechanism is a cycle in which
the output of a system “feeds back” to
either modify or reinforce the action taken
by the system.
The factor is the
condition that
changes.
The sensor detects the
change.
Feedback
Loop
The integrating center
receives the message
and activates a
response.
The effector carries
out the response.
The feedback loop means that the effector brings the factor
back to normal, which starts the whole process again.
Chunk…
 Corrective
actions that return a body
system to normal are called _____
_____.
 Define feedback mechanism.
 What are the five parts of a feedback
mechanism?
 Tell what each of these does: factor,
sensor, integrating center, effector,
feedback loop.

Our building in western Siberia is heated by a gas stove. The temperature
rises until it reaches the blue indicator on the thermostat. This switches the
heat off. Because it is a very cold day, and some heat escapes the house,
the temperature inside begins to drop. When it falls to the red indicator, the
heat is turned on. This causes the temperature to rise…
…which eventually reaches the blue indicator…
……which turns the heat off…
………which causes the temperature to fall…
…………which eventually reaches the red indicator…
……………which turns on the heat…
………………which causes the temperature to rise…
…………………

Each step causes an opposite or negative action at the next step. More heat
turns the heat off. Less heat turns the heat on.

In our animation it is possible to position the controls so that the blue turnoff indicator is below the red turn-on indicator. What do you think will
happen? Try it.
A
Thermostat detects
cooling room
temperature
Furnace turns
on to release
heat
Negative feedback
occurs as warmer
air reaches thermostat,
leading to shutting
off of furnace
Room
temperature
increases
Chunk!
 Using
the
feedback loop
diagram at the
right, explain
how a
thermostat and
furnace control
the temperature
of your house.
Negative Feedback Systems

this type of system is the most common;
a simple example is the regulation of
human body temperature
B
Brain detects
drop in blood
temperature
Nerve message
sent to muscles
to shiver
Negative feedback
occurs as warmer
blood reaches brain
sensor leading to
shut off shivers
Heat is generated that
warms body and blood
so temperature increases
Negative Feedback: Blood Glucose Levels

maintaining dynamic equilibrium often involves
interactions between cells and body organs or systems.
For example, certain cells in the body monitor the level
of glucose in the blood.
When the glucose is above its normal limits, an
endocrine organ called the pancreas secretes insulin, a
hormone that lowers blood glucose levels.
When blood glucose levels return to normal, the
pancreas stops producing insulin.
Pancreas sensor detects
high blood sugar level
Negative feedback:
lower blood sugar
leads to shutting
off of insulin
production
Pancreas
secretes
insulin
Blood sugar level drops
b/c cells take in sugar
from blood
Chunk!


What type of feedback is most common?
Give an example.
 Explain how negative feedback of body temp is
accomplished, using the terms sensor, effector, and
feedback.
 What is a two word term for homeostasis?
 Where are the sensors for blood sugar level?
 If blood sugar level gets too high, what do the
sensors do?
 What does insulin do?
 What happens when blood sugar level drops?
 What is this loop called?
Negative Feedback: Breathing Rate

Our breathing rate changes according to our
need for oxygen. During exercise, our need for
oxygen increases because we need more ATP
(energy). We are also producing more CO2 as
a waste product, which we must exhale.

The medulla in the brain constantly reads the
CO2 level in the blood and adjusts the breathing
rate accordingly. When our need for oxygen
lessens, the medulla will decrease the breathing
rate.
Negative Feedback: Plant Guard Cells

On hot, dry days plants need to conserve water.
Leaves detect a water shortage and guard cells
change shape to close the stomates to reduce
transpiration.
Once heavy water loss is no longer a threat, the
guard cells will open the stomates.
Chunk!







What is the lung factor that changes when we
exercise?
Where is the sensor for breathing rate?
What does the sensor “read”?
What does the brain tell the effectors to do?
When does the brain decrease the breathing
rate?
Explain how guard cells help a plant maintain
homeostasis, using negative feedback.
Explain how a driver trying to stay near the
speed limit is an ex of negative feedback.
Positive Feedback
When a condition is not brought back
to normal, but is reinforced by the
action, it is called positive feedback.
 The use of positive and negative is
confusing, because in most cases,
negative feedback is helpful in
maintaining homeostasis, and positive
feedback is unhealthy.

Have you ever been in an auditorium when someone steps up to a microphone
and begins to speak, only to be drowned out by a loud whistle?
Click on the image for an animation. Change the volume and see what
happens.
When the man speaks, the sound of his voice is picked up by the
microphone. It is amplified and emerges from the loudspeaker. Some
of the sound from the loudspeaker also goes into the microphone. It is
"fed back" into the amplifier circuit. If the volume is not set too high,
everything is fine. The amplifier even gets a bit of a boost by having
the microphone and speaker in the same room.
But if there is too much amplification, things go out of control. The louder
output from the speaker causes a greater input to the microphone…
…which causes a louder output from the speaker…
……which results in a greater input to the microphone…
………which causes a louder output from the speaker…
…………
The limit is that there is a maximum volume that the system can
produce. Or, someone intervenes and turns down the volume.
This is called a positive or reinforcing feedback loop. An
increase of some factor at one point in the loop causes an
increase at the next step. This can go on until some external
factor intervenes, or the process may be self-limiting.
 Consider
what would happen if you got
too hot and then put a winter coat on…
 Or if you got too cold, then went outside in
a snowstorm without a coat…
 What would a graph of your temperature
look like in each case?
Chunk!



What is positive feedback?
Is it helpful or harmful, usually?
Give an example.

Which of these lines show positive feedback?
 Which of these lines show negative feedback?
Just for fun!