Positive Feedback

Most of the body runs on negative feedback: a variable drifts from a set point, and the response pushes it back. Positive feedback works the opposite way. A change triggers a response that pushes the variable even further from where it started, and that bigger change triggers an even bigger response. The loop keeps amplifying itself in the same direction instead of settling down. This matters because it lets a cell or a body generate a fast, escalating event on purpose, something negative feedback is too stable to produce.

Childbirth contractions show this clearly. Stretching of the cervix as the baby moves down triggers release of the hormone oxytocin. Oxytocin makes the uterus contract more strongly, which stretches the cervix further, which releases more oxytocin. Each round makes the next contraction stronger, not weaker. Blood clotting runs the same logic at the cell level: a damaged vessel exposes proteins that activate nearby platelets, and activated platelets release chemical signals that activate even more platelets at that exact site, recruiting a growing plug rather than a small, stable number of cells.

Because the loop only amplifies, it never turns itself off from the inside. Something outside the loop has to remove the original trigger. Contractions stop once the baby is delivered and the cervix is no longer stretched. Clotting stops once the exposed site is completely sealed and there is no more damaged surface to activate new platelets. This is the hinge between feedback loops and the rest of cell communication: the same signal-receptor-response chain used in ordinary signaling can be wired to amplify instead of restore, and recognizing which wiring is in play tells you whether to expect a return to baseline or a runaway escalation that needs an external stop.