Anatomy and Physiology / Unit 1: Body Organization and Homeostasis
1.6 Negative and Positive Feedback
Notes
- Negative feedback reverses the original change and brings the variable back toward the set point. Most homeostatic controls use it.
- Positive feedback amplifies the change and pushes the variable further in the same direction. It is rare, short-lived and ends when the process is complete.
- Negative examples: regulation of body temperature, blood glucose (insulin lowers high glucose), blood pressure, blood calcium.
- Positive examples: labor contractions (stretching of the cervix increases oxytocin release, which strengthens contractions until birth), blood clotting, and the rising phase of a nerve impulse.
- Example: body temperature rises, the brain triggers sweating and skin vasodilation, and temperature falls back toward the set point. That is negative feedback.
Practice
After a meal, blood glucose rises and the pancreas releases insulin, which lowers blood glucose. This is an example of:
The response (insulin lowering glucose) opposes the original change, which is negative feedback.
Which process is an example of positive feedback?
In labor, contractions stimulate more oxytocin, which causes stronger contractions until birth ends the cycle.
Why is positive feedback generally not used to control body temperature?
Positive feedback amplifies a change, which would be unstable for variables that must stay within narrow limits.
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