The adrenal glands are two small, essential organs located above each kidney. They secrete severalwhich have a major role in controlling the body’s metabolism and electrolyte balance, and in stimulating important responses during . Each gland consists of two distinct parts, the outer part, or cortex, and the inner part, or medulla.
The adrenal cortex
The adrenal cortex contains three layers ofwhich secrete three types of hormones: Cortisol, also known as hydrocortisone, aldosterone, and a small amount of sex hormones. These hormones belong to a special group of compounds known as steroids, which share a common basic chemical structure. Cortisol has a major effect on the metabolism of glucose, the main fuel of the body. Its chief action is to increase glucose production by promoting the breakdown of proteins. It also enhances the mobilization and utilization of body fat. These actions provide complementary and alternative sources of energy to carbohydrates and are particularly valuable when not enough carbohydrate is available for one reason or another. Cortisol has a crucial role in promoting essential bodily responses during stresses and strains, such as illness, injury, surgery or exercise. Cortisol suppresses inflammatory reactions, which occur in the forming of immunity. This can reduce immunity however and thereby increase the risk of catching infections.
Cortisol secretion is controlled by a pituitary gland hormone called adrenocorticotropic hormone or ACTH. The level of Cortisol fluctuates according to the level of activity and stress. Aldosterone is mainly involved in the regulation of the amount of sodium and potassium in the body. When there is not enough sodium, the kidneys react by producing renin. Through various steps this hormone stimulates the secretion of aldosterone by the adrenal glands. Aldosterone acts on the kidneys again and reduces the loss of sodium in the urine. The opposite occurs when there is too much sodium in the body. Because of this influence on salt excretion, aldosterone plays an important part in the regulation of thepressure.
Because adrenocortical hormones have to perform such vital functions, it is obvious that disturbances in the function of the adrenal glands and their hormone production can cause a lot of problems. In Addison’s disease for instance, the output of aldosterone or Cortisol is too small. This leads to an abnormal amount of sodium being lost by the kidneys, resulting in lowpressure with weakness, dizziness and fainting – especially on standing. Because Cortisol is virtually absent too, the body cannot overcome even the slightest form of stress, for example as a result of simple bronchitis. Indeed such an infection might prove fatal. Replacement of the deficient hormones for life restores . But such a therapy does not provide the subtle moment-by-moment hormone regulation that normally occurs in the body. Therefore in cases where stress can be expected – such as during an operation – the replacement dose has to be adjusted.
Oversecretion by the adrenal cortex of Cortisol, especially, causes a condition known as Cushing’s syndrome. It results in weight gain and the sufferer develops a rounded and ruddy facial appearance. Some of the other symptoms include thin, weak limbs, weak bones and poor healing of wounds. Oversecretion of aldosterone alone (Conn’s syndrome) is a rare cause of highpressure.
The adrenal cortex also secretes minute amounts of sex hormones (both male and female). Under normal circumstances these hormones have little or no effect. In women the male sex hormones can induce growth of hair on places where usually only men have hair (on the chin and on the upper lip). Such a male hair-growth pattern (including balding of the scalp) tends to become more pronounced as the woman gets older.
More serious effects of the male sex hormones are acne and deepening of the voice.
Having such enormous potency in suppressing inflammatory and immune reactions, steroid hormones are widely used as drugs. In rheumatoid arthritis, steroid hormones were used for the first time. It proved to be so successful in suppressing inflammation that the drug became known as a ‘miracle drug’. Since then steroid hormones have been used increasingly to suppress inflammation, allergic reactions and the rejection of transplanted organs. Coupled to this increased use, however, was the growing awareness of all kinds of serious side-effects steroid therapy could have. Suppresion of inflammatory reactions is beneficial when dealing with rheumatoid arthritis. Inflammatory reactions are necessary however to wall off invading agents such as bacteria that have penetrated the skin. Steroid therapy may therefore encourage the spreading of bacteria, resulting in an overwhelming infection. Because of this and other side effects (for example peptic ulcers or osteoporosis) the use of corticosteroid drugs is restricted to severe disorders in which the beneficial effects justify the risks.
The adrenal medulla
The other section of the adrenal gland, the adrenal medulla, secretes adrenaline and a small amount of nor-adrenaline, which are both catecholamines. Their secretion into the bloodstream is controlled by a part of the nervous system called the sympathetic nervous system. Secretion is mainly stimulated by stress. The combined actions of adrenaline and nor-adrenaline during stress complement those of Cortisol in promoting bodily responses to deal with dangerous or threatening situations. These include an increase in heart rate and volume of blood pumped with each beat, preferential diversion of blood flow to skeletal muscles, increased breakdown of carbohydrates and fat resulting in increased glucose production, widening of tubes in the lungs (bronchial dilation), which increases oxygen supply to the lungs and, increase in metabolic rate and inhibition of bowel and bladder activity. All these are known as the ‘fight or flight’ response and are very appropriate preparation for violent physical activity of one sort or another. During stress, catecholamines, mainly nor-adrenaline, are also released in target organs from sympathetic nerve endings and so enhance the effect of circulating hormones from the adrenal medulla. Failure of the latter in disease is thus of no major consequence and replacement therapy is not required. Rarely, a tumour of the adrenal medulla may produce excessive catecholamines causing paroxysmal attacks of headache, palpitations, sweating, flushing or pallor and high blood pressure. Surgical removal of the tumour usually provides a cure.