The Role of Cortisol
The hormone cortisol has gained widespread attention as the so-called “stress hormone” because it is released in the body during stressed or agitated states. But this hormone is necessary for the functioning of almost every part of the body. Excesses or deficiencies of this crucial hormone can lead to various physical symptoms and diseases.
Cortisol is made in the adrenal glands, which are small glands adjacent to the kidneys, and it plays important roles in the regulation of blood pressure and cardiovascular function, the use of proteins, carbohydrates, and fats, in bone density, growth, kidney function, the immune system, and the brain (behaviour and cognition).
The body possesses an elaborate feedback system for controlling cortisol secretion and regulating the amount of cortisol in the blood. The pituitary gland, a small gland at the base of the brain, makes and secretes a hormone known as ACTH, which signals the adrenal glands to increase cortisol production and secretion. The hypothalamus, which is a region of the brain, signals the pituitary with CRH, to release ACTH. When the levels of the regulatory hormones ACTH and CRH increase, there is an immediate rise in cortisol levels. When cortisol is present in adequate (or excess) amounts, a negative feedback system operates on the pituitary gland and hypothalamus to reduce the output of ACTH and CRH, thereby reducing cortisol secretion by the adrenal glands.
The
body’s normal level of cortisol secretion occurs in a diurnal cycle. In
other words, cortisol levels vary during the 24-hour day. The most
active period occurs during the day, starting with the highest
concentrations in the early morning, and tapers off to the lowest by
about midnight. In addition to this normal rhythm, cortisol secretion
increases in response to any stress, whether physical or psychological.
Patients who are unable to produce enough cortisol to meet their own needs are said to have adrenal insufficiency. Adrenal insufficiency is a life-threatening hormonal deficiency which is readily treatable. Inability to produce adequate levels of cortisol can occur for various reasons.
Primary adrenal insufficiency, also called Addison’s disease, occurs when the adrenal gland is the source of the inability to produce cortisol. It is caused in most cases by the gradual destruction of the adrenal cortex, the outer layer of the adrenal glands, by the body’s own immune system. About 80 percent of reported cases in the developed world are caused by autoimmune disorders and the numbers are rising with the increase in the incidence of autoimmune diseases. Adrenal insufficiency occurs when at least 90 percent of the adrenal cortex has been destroyed. As a result, often both cortisol and the mineralocorticoid, aldostertone, are lacking. There are other causes of primary adrenal insufficiency, including tuberculosis and defective development of the adrenal glands.
Secondary adrenal insufficiency is much more common than primary adrenal insufficiency and occurs when the pituitary and hypothalamus are unable to stimulate and regulate the adrenal glands to produce cortisol. The primary causes are tumours and diseases of the pituitary.