Adrenal Glands Health Article

Definition

Adrenal glands produce and release several different hormones that maintain internal fluid levels, maintain sodium and potassium levels, and mediate the stress response.

Description

The human body contains two adrenal glands, one on top of each kidney. The gland is triangular in shape and yellowish in appearance. Subdivisions include the adrenal cortex and the medulla. The cortex is the outer layer and is responsible for the production of steroid hormones called glucocorticoids, mineralcorticoids, and androgens. The medulla forms the inner layer of the adrenal glands and releases norepinephrine and epinephrine (known commonly as noradrenaline and adrenaline) directly into the bloodstream. The adrenal cortex and medulla serve very different functions in the human body because of the different hormones that they produce and release.

Function

The adrenal cortex converts cholesterol into glucocorticoids, mineralcorticoids, and androgens. The glucocorticoids are so named due to their role in regulating body glucose levels. The major glucocorticoid produced

by the adrenal is cortisol. Cortisol is also known as the stress hormone because the body releases cortisol in order to help cope with stressful situations. The immediate effects of cortisol are to increase levels of fatty acids, proteins, and glucose in the blood. Cortisol causes these increases by taking protein from muscles, fatty acids from fatty tissues, increasing gluconeogenesis (the process of making glucose), and decreasing the body's uses of glucose. Thus, in Cushing's syndrome (hypercortisolism), patients may experience muscle wasting (too much protein is taken from the muscles). Paradoxically, although cortisol increases the levels of free fatty acids, patients with too much cortisol over a long period of time experience an increase in fat on the upper body.

Cortisol and other glucocorticoids are also potent inhibitors of the immune system. Thus, it is not too surprising that synthetic glucocorticoids, like prednisone, are used to treat autoimmune diseases and allergies— diseases in which the immune system is too active. The release of cortisol is under the control of the anterior pituitary. The anterior pituitary accomplishes this by releasing the peptide hormone, adrenocorticotropin (ACTH) onto the adrenal gland.

The mineralcorticoids are so named due to their role in establishing mineral and water levels in the body. The major mineralcorticoid produced by the adrenal gland is aldosterone (although the glucocorticoid cortisol has some mineralcorticoid activity). The primary role of aldosterone is to regulate the balance of potassium, sodium, and water by affecting the absorption of all three in the kidney. Briefly, aldosterone causes the kidney to reabsorb more water and sodium, while causing potassium to be excreted in exchange for the sodium. When too much aldosterone is produced by the adrenal glands, as in primary aldosteronism, the level of potassium in the

blood is low (hypokalemia) and the retention of sodium and water is high. Patients can experience hypertension and muscle weakness.

When there is too little aldosterone, potassium levels are high and there are extreme water and sodium losses. The loss of water and increased potassium levels can lead to extremely low blood pressure and death. A disease that might result in a loss of mineralcorticoid function is Addison's disease. In Addison's disease, the adrenals are usually at least 90% decimated before symptoms arise. The peptide, angiotensin II, and potassium levels are the main control for the release of aldosterone from the adrenals.

The adrenal glands also secrete small amounts of androgens such as testosterone. However, in the adult, that amount of androgens produced from a normally functioning adrenal gland is so small that it is unlikely to have a major effect. Nevertheless, pathology of the adrenals may result in abnormally high levels of androgens being secreted. The androgens may cause masculinization in males or females.

The adrenal medulla is really an extension of the sympathetic division of the autonomic nervous system. The sympathetic nervous system mediates "fight or flight" responses to environmental stimuli. Sympathetic nerves that originate in the spinal cord release the neurotransmitter, acetylcholine, onto the adrenal glands. The adrenal glands respond by releasing dopamine, norepinephrine, and epinephrine directly into the bloodstream. Norepinephrine and epinephrine are commonly referred to as noradrenaline and adrenaline, respectively. Epinephrine makes up the majority of the substance secreted by the adrenal medulla. Circulating norepinephrine and epinephrine can increase heart rate, constrict blood vessels, dilate eye pupils, inhibit motility and digestion in the stomach and intestines, increase sweating, increase metabolism, and increase breathing. The adrenal medulla is stimulated to release norepinephrine and epinephrine under stressful situations such as exercise or emotional distress.