The body has two adrenal glands located above the kidneys on each side. They are small, triangular shaped glands weighing a mere four to seven grams. Each is made up of an outer part called the cortex, and an inner area termed the medulla. They are quite distinct, and perform separate duties. The cortex produces an important series of hormones called steroids (due to the nature of their chemical composition). These are termed mineralocorticolds (the main one being aldosterone), glucocorticoids (the chief one being cortisol, also known as hydrocortisone), androgens (male sex hormones) and, to a lesser extent, progesterone and oestrone (female sex hormones).
The medulla produces two hormones called adrenaline and noradrenaline. These chemicals, although secreted in very small amounts, have a remarkable and profound effect on the body They are essential for the maintenance of normal function. Reduced or excessive secretion can have a dramatic effect, and in some cases may be life-threatening.
Aldosterone is the main mineralocorticold. It chiefly affects the sodium balance of the body, and may act directly on the kidneys to ascertain that normal amounts of sodium are always present in the circulating blood. In turn its activities are governed to a certain extent by the ACTH coming from the anterior pituitary. But it is also under the direct control of another hormone – renin. The rate of production of both renin and aldosterone is regulated by circulating levels of sodium. When there is a high level of sodium, the hormonal levels are low, and if there is a deficiency of sodium more renin and aldosterone are secreted, so elevating sodium levels to normal. It is a fine, delicate balance.
Cortisol (or hydrocortisone) is the main glucocorticoid secreted by the adrenal cortex. This is regulated by the amount of ACTH released by the anterior pituitary gland under the brain, which in turn is governed to a certain extent by the hypothalamus. Hormone secretion is provoked by stress factors, such as surgical operations, infections, poisonous chemicals entering the system, environmental factors, and even emotional disturbances. Temporary and rapid elevations can occur if needed. The level of circulating plasma cortisol at any time feeds back to the pituitary, and a balance of level is maintained with both the pituitary and adrenal cortex acting either to add or reduce secretion, depending on the needs at any given moment.
The hormone exerts a profound effect on the system. It helps protein breakdown into glucose (wasting, thinning of the skin and growth cessation occurring with excessive amounts circulating); it affects the rate at which water flows through the kidneys and is excreted (deficiencies make water elimination difficult).
It can affect sodium and potassium usage in the same way as does aldosterone. A deficiency reduces the body’s ability to withstand stress. Conversely an excessive amount reduces the body’s normal defensive mechanism, for it suppresses the body’s so-called immunological response. It also acts directly on the central nervous system.
For practical use, synthetic glucocorticoids have been produced and these are less potent in some of their effects. Prednisone and prednisolone have a reduced effect on sodium usage, and are therefore less likely to induce fluid retention and elevated blood pressure. They are often preferred in everyday treatment when the drug is required.
Androgens, male sex hormones, are excreted at puberty, and they play an important part in the development of the secondary sexual characteristics. These include increased bony and muscle growth, development of the scrotum, penis, prostate and voice box in the male, and vagina and clitoris in the female.
They encourage the growth of hair in the typical distribution of the mature adult. In both sexes, androgens increase sexual libido, a very important function.