A common principle that regulates the production and secretion of many hormones is the feedback loop. Often several hormones regulate each other in a chain. For example, the hypothalamic hormone corticotropin acts on the anterior pituitary to release ACTH, which acts on the adrenal cortex to release cortisol. In a feedback loop, the level of the last hormone regulates the production of earlier hormones in the loop. When cortisol blood levels increase, cortisol acts on the pituitary to decrease further ACTH secretion, which leads to a decrease in cortisol production. Acting in this way, feedback loops act to maintain hormones at a relatively constant level.