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.
Man made (synthetic) corticosteriods are used to treat a large number of conditions and symptoms. Corticosteriods are used as a replacement therapy when the body is not naturally producing enough of its own of natural corticosteriods. They are also used to treat conditions where there is inflammation, autoimmune conditions or allergy symptoms. Corticosteriod can be taken orally as a systemic treatment to treat the body as a whole or it can be applied to the affected area for a local effect as creams, inhalations, nasal sprays, eye drops, ear drops or injections. Examples of conditions they treat are allergies, asthma, COPD, dermatitis, ulcerative colitis, Crohn’s disease, multiple sclerosis, nephrotic syndrome, adrenal insufficiency, inflammation, Addison’s disease, rheumatic conditions such as arthritis, fibromyalgia and lupus.