The secretion of cortisol is mainly controlled by three inter-communicating regions of the body, the hypothalamus in the brain, the pituitary gland and the adrenal gland . This is called the hypothalamic–pituitary–adrenal axis. When cortisol levels in the blood are low, a group of cells in a region of the brain called the hypothalamus releases corticotrophin-releasing hormone , which causes the pituitary gland to secrete another hormone, adrenocorticotropic hormone , into the bloodstream. High levels of adrenocorticotropic hormone are detected in the adrenal glands and stimulate the secretion of cortisol, causing blood levels of cortisol to rise. As the cortisol levels rise, they start to block the release of corticotrophin-releasing hormone from the hypothalamus and adrenocorticotropic hormone from the pituitary. As a result the adrenocorticotropic hormone levels start to drop, which then leads to a drop in cortisol levels. This is called a negative feedback loop.
As the body's key hormones fall below the minimum required reserve for normal function and output fails, the body may down-regulate the amount needed to preserve what is on hand for only the most essential body functions . This near-failure state (Phase D) is quite serious and requires professional attention. This is a state of extreme low energy as the body tries to conserve to survive. Normally helpful nutrients may backfire with paradoxical responses being the hallmark. Those in Phase D are usually bedridden most of the time. Normal daily chores need ambulatory help. Traditional macro-nutritional approaches may be helpful. But, the body may continue to decompensate. In these cases, a carefully titrated micro-nutritional program may be necessary to help the restore the body.