The negative feedback loop is a mechanism wherein a change in some condition stimulates a response to counteract the changed condition and thereby, the homeostasis is restored.
For example, an increased blood glucose level above its homeostatic level stimulates the secretion of insulin hormone from the pancreas which in turn stimulates the absorption of glucose from the blood into the cells (specifically the liver and muscle cells) and thereby restores the normal blood glucose levels.
Most of the processes in the human body are regulated by negative feedback loops to maintain the homeostasis.
