(2) A process in which the level of one substance influences the level of another substance.
(3) A mechanism or a signal that tends to initiate (or accelerate) or to inhibit (or slow down) a process.
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.