A feedback mechanism is a loop system wherein the system responds to a perturbation. The response may be in the same direction (as in positive feedback) or in the opposite direction (as in negative feedback). In biological sense, a feedback mechanism involves a biological process, a signal, or a mechanism that tends to initiate (or accelerate) or to inhibit (or slow down) a process.
A feedback mechanism may be observed at the level of cells, organisms, ecosystems, or the biosphere. It regulates homeostasis or balance to achieve certain range or level of optimal condition. Deviation from homeostasis could eventually lead to effects detrimental to the proper functionality and organization of a system.
An example of positive feedback loop is the onset of contractions in childbirth. When contraction begins, the hormone oxytocin is released into the body to stimulate further contractions. As for the negative feedback loop, an example is the regulation of blood glucose levels. If blood glucose levels continue to rise it may result in diabetes. In fact, there are many biologic processes that use negative feedback to maintain homeostasis or dynamic equilibrium.