Positive feedback

Positive feedback is a control process in which a response amplifies the change that triggered it, driving a system farther from its initial state.

Feedback loop: A system process in which outputs return as inputs, influencing subsequent behavior. Positive feedback is one kind of loop, defined by outputs reinforcing the initiating change.
Blood clotting: The process by which blood components form a plug that limits bleeding from a damaged vessel. Activated clotting factors trigger further activation, rapidly building a clot at an injury.
Negative feedback: A control process in which a response opposes the change that triggered it. Unlike positive feedback, it counteracts deviations and commonly stabilizes a system.
Control theory: The mathematical study of how systems can be regulated through inputs, outputs, and feedback. Positive feedback is a control structure whose effects control theory analyzes.
Loop gain: The factor by which a signal changes after passing once around a feedback loop. Loop gain determines whether each pass strengthens or weakens a positive-feedback signal.
Childbirth: The process by which uterine contractions and cervical changes culminate in delivery. Cervical stretching promotes oxytocin release, which intensifies contractions and further stretching.
Homeostasis: The regulation of internal conditions within ranges compatible with an organism’s functioning. Homeostatic control often relies on negative feedback rather than self-amplifying responses.
Setpoint: A target value that a control system uses as a reference for regulation. Deviation from a reference often initiates the response that a feedback loop amplifies.
Bistability: The capacity of a system to remain in either of two stable states under the same conditions. Strong positive feedback can make two alternative states stable and enable switching between them.
Action potential: A brief electrical impulse in an excitable cell, produced by rapid changes in membrane voltage. Opening voltage-gated sodium channels depolarizes the membrane and opens still more channels.

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