Health Centres - Hypoadrenalism (underactivity of the adrenal glands)
What is hypoadrenalism?
The adrenal glands are two small but very important glands, situated one above each kidney, which produce a range of hormones, or 'chemical messengers'. Underactivity of the adrenal glands is called hypoadrenalism.
Many of the symptoms of hypoadrenalism are due to a deficiency of the steroid hormone cortisol, which is a potentially fatal deficiency if left uncorrected. Each adrenal gland consists of two parts:
- an outer ring - the cortex
- an inner core - the medulla.
The two parts have separate hormone functions and control mechanisms. The production of cortisol in the cortex is controlled by the hormone adrenocorticotropin (ACTH), which is produced by the pituitary gland at the base of the brain.
The role of the pituitary gland in adrenal function
The way in which the pituitary gland regulates the normal production of steroid hormones by the adrenal gland is through the secretion of ACTH.
If the adrenal gland produces too little cortisol, then there will be a lower level of cortisol in the blood. This is sensed by the pituitary, which therefore will increase the release of ACTH, which in turn stimulates the adrenal cortex to produce more cortisol.
Conversely, too much circulating steroid hormone will switch off the release of ACTH from the pituitary gland, which in turn reduces the adrenal gland production of steroids.
What causes hypoadrenalism?
In Addison's disease, antibodies attack the adrenal cortex, causing damage and scarring. Antibodies to the adrenal cortex can be detected in the blood of some patients.
Secondary hypoadrenalism or ACTH deficiency
Other causes
Tuberculosis destroys the whole gland, both the cortex and the medulla. There are usually signs of tuberculosis in other organs, particularly the lungs. Destruction of the adrenal glands by tuberculosis is irreversible once hormonal deficiencies are clinically detectable.
Rare causes
Secondary hypoadrenalism, or ACTH deficiency hypoadrenalism, is caused by diseases of the pituitary gland, which lead to adrenal failure as a secondary effect.
Tuberculosis of the adrenal glands may also cause hypoadrenalism. This was a common cause of Addison's disease in Britain before the 20th century and remains a major cause in underdeveloped countries.
Many rare diseases may affect the adrenals.
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