Feedback Loops

The basic machinery of regulation — a loop in which the output of a process feeds back to influence that same process.

Negative feedback

The body’s dominant mechanism. When a variable drifts from its setpoint, the response acts to reverse the change and restore balance — like a thermostat switching off the heat once a room is warm enough. Negative feedback is stabilizing: it damps fluctuations and keeps variables near their setpoint.

Nearly every homeostatic system — temperature, glucose, blood pressure, hormone levels — runs on negative feedback.

Positive feedback

The rarer mechanism. Here the response amplifies the original change, pushing the variable further from where it started. Positive feedback is destabilizing by design, so the body reserves it for processes that need to run to a rapid, decisive completion:

• Childbirth — contractions trigger more contractions until delivery.
• Blood clotting — each step accelerates the next until the leak is sealed.
• The nerve impulse — a small trigger explodes into a full signal.

Each positive loop has a clear endpoint that ends the cycle.

Key idea

The difference is direction: negative feedback opposes change to hold things steady; positive feedback reinforces change to drive an event to completion. The body relies overwhelmingly on the first.