FEEDBACK MECHANISMS

Mr. MahLiving Environment

Lecture 10

Warm-Up Quiz Hormones are secreted by

endocrine glands or cells into the blood. Only _____________ ___________with receptors for the hormone will respond to the signal.TARGET CELLS

What are the two places you can find cell receptors?Cell SurfaceInside the Cell

FEEDBACK MECHANISMS

Mr. MahLiving Environment

Lecture 10

SWBAT evaluate a disruption in homeostasis and explain, through the use of a feedback mechanism, how the body compensates.

Homeostasis

Body's ability to maintain stable internal environment

Typically maintained with communication of the nervous and endocrine systems

Think about thirst, blood sugar, and body temperature?

Also known as Dynamic Equilibrium

Dynamic Equilibrium A balance between two opposite

reactions. Dynamic because there are changes

taking place. Equilibrium because there is a balance

Feedback Mechanism A release of chemicals or a reaction that helps

maintain equilibrium with in a system.

Example: hammer to knee  A change in the environment is called a

stimulus.  A response is the manner in which the

organism reacts to the stimulus.  (knee jerk reflex)

Ex. cold, hot, fear

Homeostasis Control Mechanisms

The variable produces a change in the body

The three interdependent components of control mechanisms are:

Receptor – monitors the environment and responds to changes (stimuli)

Control center – determines the level of response to the stimulus

Effector – provides the actual response

Stimulus:Produceschangein variable

1

2

3

Changedetectedby receptor

Input:Informationsent alongpathway to Control Center

5Response ofeffector feedsback to influencemagnitude of stimulus andreturnsvariable tohomeostasis

Variable (in homeostasis)

Imbalance

Imbalance

Receptor (sensor)

Controlcenter

4

Output:Information sentalong pathway to Effector

Effector

Homeostatic Control Mechanisms

Feedback

The response either depresses (negative) or enhances (positive) the stimulusNegative Feedback

Response turns off stimulus (ex. your air conditioning at home, heart rate, breathing rate, oxygen)

Positive Feedback Response increases stimulus Rare in body (ex. Blood clotting)

Negative Feedback

• Prevents sudden, severe changes in the body

• Corrects the set point (balance point)• Causes opposite of bodily disruption to

occur, i.e. the ‘negative’• Limits chaos in the body by creating

stability• Most common type of feedback loop• Examples: body temperature, blood

pressure & glucose regulation

Negative Feedback

Negative Feedback

• Increases (accelerates) the actions of the body

• Produces more instability in the body

• Produces more chaos in the body

• There are only a few types necessary for our survival

• Positive feedback mechanisms are short-lived

• Controls only infrequent events that do not require continuous adjustments

• Considered to be the uncommon loop

• Examples: blood clotting and child birth

Positive Feedback

Positive Feedback In positive

feedback systems, the output enhances or exaggerates the original stimulus

Example: Regulation of blood clotting

Figure 1.6

Maintenance of Life

Receptors

Control center(set point)

Effectors(muscles or glands)

Response(Change is corrected.)

Stimulus(Change occursin internalenvironment.)

(Change is comparedto the set point.)

Homeostatic Imbalance

Disturbance of homeostasis or the body’s normal equilibrium

Overwhelming of negative feedback mechanisms allowing destructive positive feedback mechanisms to take over

Thyroid Problems

What would happen if the thyroid could no longer produce its hormones?

No negative feedback to hypothalamus and anterior pituitary

Goiter

Hypersecretion of TSH or TH