Cortisol is a hormone that is produced by the outer cortex of the adrenal gland. Cortisol is referred to as a glucocorticoid because it causes an increase in blood glucose. It also stimulates the release of some amino acids from muscle tissue and fatty acids from fat tissue. The amino acids are then converted in the liver to glucose, which can be used by the brain.

The important functions of cortisol include:

• Assisting the body in its response to stress
• Carbohydrate and fat metabolism
• Helping balance the effects of insulin in breaking down sugar for energy
• Helping the immune system's inflammatory response
• Maintaining blood pressure and cardiovascular function
• Regulation of protein

The pituitary gland regulates glucocorticoid production by its production of adrenocorticotropic hormone (ACTH). This hormone stimulates the adrenal glands to produce cortisol. Excessive ACTH produced by a tumor in the pituitary gland or an overactive adrenal gland can cause high levels of cortisol.