Feedforward Loops

Positive feed-forward loops are inherently unstable, but feedforward loops are common in endocrine and metabolic control systems. Positive feed-forward signals may increase flow through a metabolic sequence. Positive feedback occurs during blood clotting. The clotting sequence is inactive at rest, but once triggered, the cascade of clotting factors goes to completion, amplifying the original signal. The process self-limits as the clotting factors get used up.

If we disturb a system, and a variable remains constant, we expect to find negative feedback controlling that variable. If, on the other hand, a variable suddenly and rapidly increases or decreases, we expect to find positive feedback.

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