4.5 Feedback

Negative feedback

A feedback loop is when the output of a process loops back to influence it. Negative feedback *counteracts* a change, pushing conditions back toward a set point — this maintains homeostasis. Examples: blood glucose control (insulin/glucagon) and body temperature regulation.

Positive feedback

Positive feedback *amplifies* a change, driving a process to completion. It's less common. Examples: childbirth (oxytocin increases contractions, which increase oxytocin), blood clotting, and the release of milk during nursing.

Key terms

Negative feedback

A loop that counteracts a change to restore the set point (maintains homeostasis).

Positive feedback

A loop that amplifies a change, driving a process to completion.

Homeostasis

The maintenance of stable internal conditions, mainly by negative feedback.

Set point

The target value a negative-feedback system works to maintain.

Positive feedback example

Childbirth (oxytocin), blood clotting, and milk release during nursing.

Try an AP-style question

After a meal, blood glucose rises, insulin is released, and glucose levels fall back toward normal. This is an example of…

1. negative feedback maintaining homeostasis
2. positive feedback amplifying a change
3. positive feedback returning to a set point
4. a signaling pathway with no feedback