Connect!Connect!

How does your body react to being cold?How does your body react to being cold?

What happens once you warm up?What happens once you warm up?

Explain how a thermostat and furnace work Explain how a thermostat and furnace work together to keep your house temperature together to keep your house temperature within a narrow range.within a narrow range.

Feedback MechanismsFeedback Mechanisms

As mentioned previously, organisms As mentioned previously, organisms constantly monitor and constantly monitor and adjustadjust to changes to changes in the external and internal environments. in the external and internal environments.

Often when a change is detected a Often when a change is detected a corrective action must be taken that corrective action must be taken that returns the organism’s systems to returns the organism’s systems to normalnormal. . These actions are called These actions are called feedback feedback mechanisms. mechanisms.

a feedback mechanism is a cycle in which a feedback mechanism is a cycle in which the output of a system the output of a system “feeds back”“feeds back” to to either modify or reinforce the action taken either modify or reinforce the action taken by the system. by the system.

The factor is the The factor is the condition that condition that changes.changes.

The sensor detects the The sensor detects the change.change.

The integrating center The integrating center receives the message receives the message and activates a and activates a response.response.

The effector carries The effector carries out the response.out the response.

Feedback Loop

The feedback loop means that the effector brings the factor back to normal, which starts the whole process again.

Chunk…Chunk…

Corrective actions that return a body Corrective actions that return a body system to normal are called _____ system to normal are called _____ _____._____.

Define feedback mechanism.Define feedback mechanism. What are the five parts of a feedback What are the five parts of a feedback

mechanism?mechanism? Tell what each of these does: factor, Tell what each of these does: factor,

sensor, integrating center, effector, sensor, integrating center, effector, feedback loop.feedback loop.

Our building in western Siberia is heated by a gas stove. The temperature 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 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, 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 the temperature inside begins to drop. When it falls to the red indicator, the heat is turned on. This causes the temperature to rise…heat is turned on. This causes the temperature to rise……which eventually reaches the blue indicator……which eventually reaches the blue indicator………which turns the heat off………which turns the heat off…………which causes the temperature to fall…………which causes the temperature to fall……………which eventually reaches the red indicator……………which eventually reaches the red indicator………………which turns on the heat………………which turns on the heat…………………which causes the temperature to rise…………………which causes the temperature to rise………………………………………

Each step causes an opposite or negative action at the next step. More heat Each step causes an opposite or negative action at the next step. More heat turns the heat off. Less heat turns the heat on.turns the heat off. Less heat turns the heat on.

In our animation it is possible to position the controls so that the blue turn-off In our animation it is possible to position the controls so that the blue turn-off indicator is below the red turn-on indicator. What do you think will happen? indicator is below the red turn-on indicator. What do you think will happen? Try it.Try it.

AAThermostat detectsThermostat detects

cooling room cooling room temperaturetemperature

Furnace turnsFurnace turns Negative feedback Negative feedbackon to releaseon to release occurs as warmeroccurs as warmer heatheat air reaches air reaches

thermostat, thermostat, leading to leading to

shuttingshuttingoff of furnaceoff of furnace

RoomRoomtemperaturetemperatureincreasesincreases

Using the Using the feedback loop feedback loop diagram at the diagram at the right, explain right, explain how a how a thermostat and thermostat and furnace control furnace control the temperature the temperature of your house.of your house.

Chunk!

Negative Feedback SystemsNegative Feedback Systems

this type of system is the most common; this type of system is the most common; a simple example is the regulation of a simple example is the regulation of human body human body temperaturetemperature

BBBrain detectsBrain detectsdrop in blood drop in blood temperaturetemperature

Nerve messageNerve message Negative feedback Negative feedbacksent to musclessent to muscles occurs as warmeroccurs as warmer to shiverto shiver blood reaches brain blood reaches brain

sensor leading tosensor leading toshut off shiversshut off shivers

Heat is generated thatHeat is generated thatwarms body and bloodwarms body and blood

so temperature increasesso temperature increases

Negative Feedback: Blood Glucose Negative Feedback: Blood Glucose LevelsLevels

maintaining dynamic maintaining dynamic equilibriumequilibrium often involves often involves interactions between cells and body organs or systems. interactions between cells and body organs or systems.

For example, certain cells in the body monitor the level For example, certain cells in the body monitor the level of glucose in the of glucose in the bloodblood. .

When the glucose is above its normal limits, an When the glucose is above its normal limits, an endocrine organ called the endocrine organ called the pancreaspancreas secretes insulin, a secretes insulin, a hormone that hormone that lowerslowers blood glucose levels. blood glucose levels.

When blood glucose levels return to normal, the When blood glucose levels return to normal, the pancreas stops producing pancreas stops producing insulininsulin. .

PancreasPancreas sensor detects sensor detectshigh blood sugar level high blood sugar level

Negative Negative feedback:feedback:

PancreasPancreas lower blood sugarlower blood sugar secretessecretes leads to shutting leads to shutting

insulininsulin off of insulin off of insulin productionproduction

Blood sugar level dropsBlood sugar level dropsb/c cells take in sugarb/c cells take in sugar

from bloodfrom blood

Chunk!Chunk! What type of feedback is most common?What type of feedback is most common? Give an example.Give an example. Explain how negative feedback of body temp is Explain how negative feedback of body temp is

accomplished, using the terms sensor, effector, and accomplished, using the terms sensor, effector, and feedback.feedback.

What is a two word term for homeostasis?What is a two word term for homeostasis? Where are the sensors for blood sugar level?Where are the sensors for blood sugar level? If blood sugar level gets too high, what do the If blood sugar level gets too high, what do the

sensors do?sensors do? What does insulin do?What does insulin do? What happens when blood sugar level drops?What happens when blood sugar level drops? What is this loop called?What is this loop called?

Negative Feedback: Breathing RateNegative Feedback: Breathing Rate

Our breathing rate Our breathing rate changeschanges according to our according to our need for oxygen. During exercise, our need for need for oxygen. During exercise, our need for oxygen increases because we need more ATP oxygen increases because we need more ATP ((energy)energy). We are also producing more CO. We are also producing more CO22 as a as a waste product, waste product, which we must exhale.which we must exhale.

The medulla in the brain constantly reads the The medulla in the brain constantly reads the COCO2 2 level in the blood and adjusts the breathing level in the blood and adjusts the breathing rate accordingly. When our need for oxygen rate accordingly. When our need for oxygen lessens, the medulla will decrease the breathing lessens, the medulla will decrease the breathing rate.rate.

Negative Feedback: Plant Guard CellsNegative Feedback: Plant Guard Cells

On hot, dry days plants need to conserve water.On hot, dry days plants need to conserve water.

Leaves detect a water shortage and guard cells Leaves detect a water shortage and guard cells change shape to close the stomates to reduce change shape to close the stomates to reduce transpiration. transpiration.

Once heavy water loss is no longer a threat, the Once heavy water loss is no longer a threat, the guard cells will open the stomates.guard cells will open the stomates.

What is the lung factor that changes when we What is the lung factor that changes when we exercise?exercise?

Where is the sensor for breathing rate?Where is the sensor for breathing rate? What does the sensor “read”?What does the sensor “read”? What does the brain tell the effectors to do?What does the brain tell the effectors to do? When does the brain decrease the breathing When does the brain decrease the breathing

rate?rate? Explain how guard cells help a plant maintain Explain how guard cells help a plant maintain

homeostasis, using negative feedback.homeostasis, using negative feedback. Explain how a driver trying to stay near the speed Explain how a driver trying to stay near the speed

limit is an ex of negative feedback.limit is an ex of negative feedback.

Chunk!

Positive FeedbackPositive Feedback

When a condition is not brought back When a condition is not brought back to normal, but is reinforced by the to normal, but is reinforced by the action, it is called positive feedback.action, it is called positive feedback.

The use of positive and negative is The use of positive and negative is confusing, because in most cases, confusing, because in most cases, negative feedback is helpful in negative feedback is helpful in maintaining homeostasis, and positive maintaining homeostasis, and positive feedback is unhealthy.feedback is unhealthy.

Have you ever been in an auditorium when someone steps up to a microphone 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?and begins to speak, only to be drowned out by a loud whistle?

Click on the image Click on the image for an animation. Change the volume and see what for an animation. Change the volume and see what happens.happens.

When the man speaks, the sound of his voice is picked up by the 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 microphone. It is amplified and emerges from the loudspeaker. Some of the sound from the loudspeaker also goes into the microphone. It is "fed 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, 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 everything is fine. The amplifier even gets a bit of a boost by having the microphone and speaker in the same room.microphone and speaker in the same room.

But if there is too much amplification, things go out of control. The louder 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…output from the speaker causes a greater input to the microphone…

… …which causes a louder output from the speaker…which causes a louder output from the speaker………which results in a greater input to the microphone………which results in a greater input to the microphone…………which causes a louder output from the speaker…………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 Consider what would happen if you got too hot and then put a winter coat on…too hot and then put a winter coat on…

Or if you got too cold, then went outside in Or if you got too cold, then went outside in a snowstorm without a coat…a snowstorm without a coat…

What would a graph of your temperature What would a graph of your temperature look like in each case?look like in each case?

Chunk!Chunk!

What is positive feedback?What is positive feedback? Is it helpful or harmful, usually?Is it helpful or harmful, usually? Give an example.Give an example.

Which of these lines show positive feedback?Which of these lines show positive feedback? Which of these lines show negative feedback?Which of these lines show negative feedback?

Just for fun!Just for fun!