There are two adrenal glands in the body. They sit just on top of and in front of the two kidneys. Each gland is about 5cm (2 inches) tall, 3cm (just over an inch) wide and measures about 1cm (just under half an inch) from front to back.

The glands are formed of an outer layer called the cortex and an inner core called the medulla. The medulla makes up about 10% of each of the glands.

Although they are small the adrenal glands are very important as they produce a number of vital hormones.

The cortex produces three types of hormone:

• glucocorticoids: the most important of these is cortisol or hydrocortisone. The effects of these hormones are very complex and include helping to convert protein to carbohydrate, controlling the balance of potassium, sodium and glucose in the body and have effects on the lymphatic and immune systems.

• mineralocorticoids: the most important of these is aldosterone. These hormones regulate the balance of potassium and sodium in the body, which maintains the amount of blood in the heart and circulatory system and regulates blood pressure.

• sex hormones: although the male hormones (androgens) and female hormones (oestrogen and progesterone) are mainly produced by the testes and ovary respectively, the adrenal cortex does produce small quantities of these hormones.

The hormones produced by the adrenal cortex are known collectively as corticosteroids. The word 'steroids' is often used as description of certain drugs and this usually refers to synthetic versions of the glucocorticoids, drugs like prednisolone, prednisone and dexamethasone.

The adrenal medulla produces the hormones adrenaline and nor-adrenaline. These lead to changes including increased heart rate, increased blood supply to vital organs, slowing of digestion, sweating and dilatation of the pupils. Because these effects are important in helping the body to deal with emergencies, adrenaline and nor-adrenaline are sometimes called the hormones of 'fight or flight'.

Tumours of the adrenal gland can develop in either the cortex or the medulla. Adrenal cortical tumours may be either benign (non-cancerous) in which case they are called adenomas, or cancerous (malignant) in which case they are called adrenal cortical carcinomas. Tumours of the medulla are called phaeochromocytomas, these are usually benign but may occasionally be malignant.