Regulation
Cortisol is a hormone that, according to the Cambridge Encyclopedia, has a natural cycling in the body known as diurnal variation which means that its levels are partly controlled by sleeping. Normally, cortisol is at its highest levels in the early morning and reaches its lowest daily levels after a person has been asleep for a few hours. Cortisol levels can be elevated by depression and psychological stress, as well as physiological stress. Examples of physiological stress include illness, fever, trauma, physical exertion and invasive medical procedures (such as surgery).
Glucose and Electrolytes
As an article in "Postgraduate Medicine" explains, one way in which cortisol works is by elevating blood glucose levels. It does this by counteracting the effects of insulin. Insulin is a hormone that stimulates fat and muscle cells to take in glucose from the blood. By counteracting this hormone, cortisol makes more glucose available in the blood for other tissues (such as the brain). Cortisol also regulates the levels of certain electrolytes (such as sodium and potassium) in the blood. It prompts the intestines to absorb more sodium, and it signals the kidneys to excrete additional potassium via the urine.
Immune Effects
Another way in which cortisol works is by suppressing the immune system. T-cells are a type of cell which plays a major role in inflammation and immune system responses. Cortisol has the ability to block the ability of some T-cells to produce chemicals that the immune system uses to cause inflammation and immune responses. For this reason, cortisol is often given (orally, via injection or topically) to block the immune system's response. It is particularly useful in treating conditions caused by inflammation, including allergic rashes and some forms of arthritis.
