Negative feedback loops are a series of self-regulated pathways designed by the body to prevent the excessive production of hormones and other biochemicals. Using the example to the right, A (stimulus) activates B (sensor), B activates C (control), and C activates D (effector). D is the final product. Once enough of product D is made, product D then acts as an inhibitor to reactant A to shut down the pathway. If there are still insufficient amounts of product D, then the pathway is still active and continues to make product D until homeostatic conditions are met to meet the demands of the current situation.
Example: Cortisol is needed by the body because of low blood sugar or some stressful event. CRH is released, to stimulate ACTH, which stimulates cortisol. When enough cortisol is produced, cortisol acts as an inhibitor to the hypothalamus "saying" that enough cortisol is produced and the pathway ends.
