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. 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 factor is the condition that changes. The sensor detects the change. The sensor detects the change. The integrating center receives the message and activates a response. The integrating center receives the message and activates a response. The effector carries out the response. The effector carries 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…  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 turn- off indicator is below the red turn-on indicator. What do you think will happen? Try it.

A Thermostat detects cooling room temperature Furnace turns Negative feedback on to releaseoccurs as warmer heat air reaches thermostat, heat air reaches thermostat, leading to shutting leading to shutting off of furnace Roomtemperatureincreases

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

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 Negative feedback sent to musclesoccurs as warmer to shiver blood reaches brain to shiver blood reaches brain sensor leading to 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: Negative feedback: Pancreaslower blood sugar Pancreaslower blood sugar secretes leads to shutting secretes leads to shutting insulin off of insulin production production 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 CO 2 as a waste product, which we must exhale.  The medulla in the brain constantly reads the CO 2 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. 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. Once heavy water loss is no longer a threat, the guard cells will open the stomates.

 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. Chunk!

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