A negative feedback mechanism works something like a thermostat in your home. A thermostat helps maintain a constant temperature, called the normal range. When the temperature rises beyond the normal range, the thermostat turns on the air conditioner. Eventually the air conditioner restores the temperature to the normal range. This process is called negative feedback. It starts with a normal range, goes beyond the normal range, and then back to normal again.
An example of how negative feedback works in the body can be demonstrated by the endocrine system’s controls over the amount of sugar in the bloodstream. Insulin is a hormone secreted by the pancreas that maintains a normal amount of sugar in the bloodstream. Shortly after eating a candy bar, tiny sugar molecules enter the bloodstream raising the blood sugar levels. In response, the pancreas secretes the insulin into the bloodstream. Now, the sugar molecules move out of the bloodstream and into the cells of the skeletal muscles, fat and liver. In turn, the blood sugar levels return to normal. Unsupported extension