The adrenal glands are located on top of each of the kidneys and serve a variety of functions in the human body. The adrenal cortex releases products like the aldosterone (a mineralocorticoid), cortisol (glucocorticoid), dehydroepiandrosterone (DHEA, an androgen), DHEA sulfate (DHEAS) and androstenedione (also an androgen). The adrenal medulla secrets substances such as epinephrine, norepinephrine and dopamine; these substances are known as catecholamines.
Aldosterone
Aldosterone is a hormone whose main function is to reabsorb sodium and water at the level of the kidneys. It also causes the excretion of potassium and hydrogen ions at the same time. Thus, it is primarily used by the body to increase blood pressure, and its release is controlled by a variety of body systems such as the hormones renin and angiotensin, sympathetic nervous system nerves and sensors in the body that react to electrolyte levels in serum (such as sodium and potassium).
Cortisol
This glucocorticoid is also known as the "stress hormone" and has a variety of functions. It counteracts insulin and increases blood sugar via effects on the liver, increases levels of stomach acid, weakens the activity of the immune system, lowers bone formation, increases the sensitivity of blood vessels to other stimulants (such as epinephrine) and causes decreased collagen in the skin. Its release is primarily controlled by the pituitary gland and its release of ACTH (a hormone that stimulates cortisol release).
Androgens
DHEA, DHEAS and androstenedione are the androgen hormones, which basically mean they stimulate and maintain masculine characteristics. Ironically, they are converted into and are thus the precursors of the estrogens, which are the female sex hormones. They play a major role in the development of the male, which include formation of the testes and the masculinization of the male fetus. In adult males, they serve to develop the secondary sex characteristics like increased muscle mass and decreased fat deposition, as well as help the body develop during male puberty. Female effects include masculinization, such as frontal balding, clitoral enlargement, increased muscle mass and a deep voice.
Epinephrine
This is also known as adrenaline and is a powerful short-term stress hormone. It is released during "fight-or-flight" stressors and acts on B1, B2, A1 and A2 adrenergic receptors. B1 effects include increased heart rate and contractility, while B2 stimulation results in blood vessel dilation and bronchi dilation in the lungs. A1 stimulation results constriction of blood vessels (stronger than the B2 effect of dilation), and A2 serves to decrease the release of further stress hormones but has a minimal effect with epinephrine.
Norephinephrine
This stress hormone is similar to epinephrine, except that it stimulates B1, B2 and A1 receptors (not A2). The results in the body are similar to that of epinephrine, as they stimulate almost the same receptors.
Dopamine
Dopamine in the brain has a very different function, and systemic dopamine does not cross into the brain, instead exerting its effects on the rest of the body. At low dosages, it binds D1 receptors, resulting in blood vessel dilation and increased blood to the renal, coronary and digestive system arteries. At higher dosages, it also binds B1 receptors and thus causes increased heart rate and contractility. At even higher dosages, it tends to binds A1 receptors and causes widespread blood vessel constriction, increasing blood pressure. Excessive A1 stimulation can result in constriction of the blood vessels to the kidney to the point that they are damaged, so care must be taken.
References
- "Campbell-Walsh Urology, 9th Edition;" Wein; 2007
- "Cecil Medicine, 23rd Edition;" Goldman; 2007
- "Williams Textbook of Endocrinology, 11th Edition;" Kronenberg; 2008
