The adrenal glands are the endocrine glands located at the top of each kidney: they are composed of the outer layer called the cortex and the inner layer known as the medulla; they secrete hormones that are released into the bloodstream.
The adrenal cortex produces over two dozen different steroid hormones and structurally is divided into three distinct regions or zones:
- An outer spiral zone (the zona glomerulosa) that produces mineralocorticoids (mainly aldosterone);
- A central zone, the cells organized into bundles or ‘fascicles’ (the zona fasciculata), that produces glucocorticoids (mainly cortisol, corticosterone and cortisone);
- An inner zone, its cells arranged in cords that give a net-like appearance (the zona reticularis) that produces androgens.
The adrenal medulla occupies the centre of the gland and produces adrenaline (epinephrine) and noradrenaline (norepinephrine).
Α) The hormone cortisol is synthesized by the adrenal cortex. It is known as the ‘stress hormone’ because stress activates cortisol secretion. When cortisol levels are above average or much elevated over a long period of time (as for instance in chronic stress and depression), this induces negative effects and endangers health. The state of prolonged hyper/overfunction of the adrenal cortex and elevated levels of cortisol is named Cushing’s or Cushing syndrome or disease. The patient with this condition manifests central fatty deposition, muscle weakness, insulin resistance, elevated blood sugar, high blood pressure, thinning and fragile skin, vascular and coagulation disorders, hirsutism, pink/purple stretch marks (striae) on the skin (abdomen, thighs, breast, arms). The state of inadequate cortisol secretion by the adrenal glands is called Addison’s or Addison syndrome or disease. Its main cause is an idiopathic autoimmune mechanism as well as stressful events such as infections and surgery, taking of coagulants (blood thinners), certain medications, neoplasms, haemorrhage, storage diseases. The patient suffers from fatigue, orthostatic hypotension (head rushes, dizzy spells), vomiting, decreased appetite, weight loss, hyperpigmentation (darkening of the skin). Addison’s disease may be accompanied by other autoimmune diseases, as hypothyroidism, vitiligo (skin depigmentation), ovary deficiency / amenorrhoea, small testicles, impotence.
Β) Pheochromocytoma is a neuroendocrine tumour of the medulla of the adrenal glands or, less commonly, in the ganglia of the sympathetic nervous system. These tumours secrete high amounts of catecholamines (mainly norepinephrine, and, to a lesser degree, epinephrine). The symptoms of pheochromocytoma are of a very large variety and are often quite dramatic. The most frequent of these are headache, diaphoresis (excessive sweating) and palpitations. Sometimes there are also severe hot flashes, anxiety (often resembling a panic attack), stress and irritability, all of which often complicate diagnosis. Over 90% of patients are hypertensive. Occasionally (10% of cases), the endocrine tumour is extra-adrenal, i.e. it is located outside the gland, in which case it is called a paraganglioma
The only effective treatment is surgical excision of the tumour. After successful surgery, the patient will require long-term monitoring.
C) Aldosterone is a steroid hormone belonging to the mineralocorticoid family that is produced by the adrenals. Mainly through its action on the distal tubules and collecting ducts of the nephron, i.e. the functional unit of the kidney, it causes reabsorption of sodium and water, secretion of potassium and increase in arterial pressure.
Primary hyperaldosteronism is an elevated production of aldosterone in the adrenals. In recent years, studies have shown that about one in ten hypertensive patients suffer from primary hyperaldosteronism. Risk of cardiac diseases and stroke appears to be higher in these patients as compared with others with hypertension.
Common diseases of the adrenal glands that cause primary aldosteronism are the following:
- Idiopathic bilateral adrenal hyperplasia: this denotes hyperactivity in both adrenals and is the most common cause of primary hyperaldosteronism, occurring in two thirds of all cases. In a few cases, the hyperplasia is not visible on X-ray images.
- Conn’s or Conn syndrome: This is a benign tumour in one of the two adrenals; it is observed in one third of all cases.
- Hypoalderosteronism: This is the insufficient production of aldosterone by one of the adrenals; it is a rare complaint.
D) Congenital adrenal hyperplasia: This is a genetic disorder inherited as an autosomal recessive trait. It arises through a deficiency of one of the enzymes necessary for the synthesis of cortisol.
Deficiency of 21-hydrolyxase is the commonest disorder and is present in 90-95% of cases. Because of their inability to produce cortisol, the adrenals produce other forms of corticoids that exert androgenizing action. In its severest form, the disease is accompanied by aldosterone insufficiency and salt loss / salt wasting as from birth; the non-classical form, which is more common, may be asymptomatic or else be accompanied by elevated androgens. Physical development, genitals, reproductive functioning can all be affected by the disruption in the metabolism of these hormones.
Ε) Νeoplasms that metastatize to the adrenals mainly originate from the lungs, breast and intestine. Cancers originating from the adrenals themselves are fairly rare.
F) Incidentally discovered adrenal masses (incidentalomas): Quite frequently, tumours are detected in the adrenals which however are benign and do not produce hormones. The endocrinologist will undertake the necessary hormonal assessment so as to determine hormone secretion as well as X-ray checks in order to track tumour growth.
Diagnosis and treatment of adrenal diseases
Diagnosis of the above hormonal disorders often requires specific hormone tests, the choice of test being at the discretion of the endocrinologist. In numerous cases, X-ray investigation of these conditions necessitates specialized radiologic methods.
Treatment tailored to the particular case may be medical (treatment of hormone disruptions; treatment of complications) or alternatively surgical.