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Chapter: Medical Physiology: Adrenocortical Hormones

Hypoadrenalism-Addison’s Disease

Addison’s disease results from failure of the adrenal cortices to produce adrenocortical hormones, and this in turn is most frequently caused by primary atrophy of the adrenal cortices.

Hypoadrenalism-Addison’s Disease

Addison’s disease results from failure of the adrenal cortices to produce adrenocortical hormones, and this in turn is most frequently caused by primary atrophy of the adrenal cortices. In about 80 per cent of the cases, the atrophy is caused by autoimmunity against the cor-tices. Adrenal gland hypofunction is also frequently caused by tuberculous destruction of the adrenal glands or invasion of the adrenal cortices by cancer. The dis-turbances in Addison’s disease are as follows.

Mineralocorticoid Deficiency. Lack of aldosterone secre-tion greatly decreases renal tubular sodium reabsorp-tion and consequently allows sodium ions, chloride ions, and water to be lost into urine in great profusion. The net result is a greatly decreased extracellular fluid volume. Furthermore, hyponatremia, hyperkalemia, and mild acidosis develop because of failure of potassium and hydrogen ions to be secreted in exchange for sodium reabsorption.

As the extracellular fluid becomes depleted, plasma volume falls, red blood cell concentration rises markedly, cardiac output decreases, and the patient dies in shock, death usually occurring in the untreated patient 4 days to 2 weeks after cessation of mineralo-corticoid secretion.

Glucocorticoid Deficiency. Loss of cortisol secretion makesit impossible for a person with Addison’s disease to maintain normal blood glucose concentration between meals because he or she cannot synthesize significant quantities of glucose by gluconeogenesis. Furthermore, lack of cortisol reduces the mobilization of both proteins and fats from the tissues, thereby depressing many other metabolic functions of the body. This sluggishness of energy mobilization when cortisol is not available is one of the major detrimental effects of glu-cocorticoid lack. Even when excess quantities of glucose and other nutrients are available, the person’s muscles are weak, indicating that glucocorticoids are needed to maintain other metabolic functions of the tissues in addition to energy metabolism.

Lack of adequate glucocorticoid secretion also makes a person with Addison’s disease highly susceptible to the deteriorating effects of different types of stress, and even a mild respiratory infection can cause death.

Melanin Pigmentation. Another characteristic of mostpeople with Addison’s disease is melanin pigmentation of the mucous membranes and skin. This melanin is not always deposited evenly but occasionally is deposited in blotches, and it is deposited especially in the thin skin areas, such as the mucous membranes of the lips and the thin skin of the nipples.

The cause of the melanin deposition is believed to be the following: When cortisol secretion is depressed, the normal negative feedback to the hypothalamus and anterior pituitary gland is also depressed, therefore allowing tremendous rates of ACTH secretion as well as simultaneous secretion of increased amounts of MSH. Probably the tremendous amounts of ACTH cause most of the pigmenting effect because they can stimulate formation of melanin by the melanocytes in the same way that MSH does.

Treatment of People with Addison’s Disease. An untreatedperson with total adrenal destruction dies within a few days to a few weeks because of weakness and usually circulatory shock. Yet such a person can live for years if small quantities of mineralocorticoids and glucocorti-coids are administered daily.

Addisonian Crisis. As noted earlier, greatquantities of glucocorticoids are occasionally secreted in response to different types of physical or mental stress. In a person with Addison’s disease, the output of glucocorticoids does not increase during stress. Yet whenever different types of trauma, disease, or other stresses, such as surgical operations, supervene, a person is likely to have an acute need for excessive amounts of glucocorticoids and often must be given 10 or more times the normal quantities of glucocorticoids to prevent death.

This critical need for extra glucocorticoids and the associated severe debility in times of stress is called an addisonian crisis.

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