What do Adrenal Glands Do?Adrenal glands produce hormones required for healthy life. The adrenal cortex produces hormones that controls sex (androgens, estrogens), salt balance in the blood (aldosterone), and sugar balance (cortisol). The adrenal medulla produces hormones involved in the fight-or-flight response (catecholamines, or adrenaline type hormones such as epinephrine and norepinephrine).
The Adrenal Medulla and Cortex Produce Very Different Hormones. We have two adrenal glands located on the top of both kidneys. They are triangular-shaped and about the size and color of a fortune cookie. Each gland consists of a medulla (the center of the gland) which is surrounded by the cortex.
Function of the Adrenal Medulla.The adrenal medulla is responsible for producing catecholamines, or adrenaline-type hormones such as epinephrine and norepinephrine. We have all experienced that sudden panic feeling and anxiety when something happens suddenly and unexpectedly and we get scared. All of a sudden we have tingles and we feel like we need to run away or stand up and fight. This is the "fight-or-flight" symptoms and it is caused by the sudden release of adrenaline from our adrenal glands. (yes, adrenaline is called this because it comes from the adrenal gland). Adrenaline as we call it generically can be broken down into two different hormones that the adrenal medulla produces: epinephrine and norepinephrine.
Function of the Adrenal Cortex.The adrenal cortex produces a handful of hormones necessary for fluid and electrolyte (salt) balance in the body such as cortisol and aldosterone. The adrenal cortex also makes small amounts of sex hormones but this only becomes important if overproduction is present (most sex hormones are produced by the testes and ovaries). The three layers of the adrenal cortex are:
- The zona glomerulosa (ZG) is the most superficial layer of the adrenal cortex and it produces the hormone aldosterone as well as some small amounts of progesterone (a sex hormone). The mineralocorticoid aldosterone is produced here.
- The zona fasciculata (ZF) is the middle zone of the adrenal cortex, and it primarily produces cortisol.
- The zona reticularis (ZR) is the inner most zone of the adrenal cortex and it is adjacent to the adrenal medulla. The functions of the zona reticularis are to store cholesterol for steroidogenesis (the making of steroid hormones) and the secretion of sex hormones such as estrogen, and testosterone (in small amounts).
Technical Information for Doctors and Nurses.
In the zona glomerulosa (ZG), progesterone is converted through several steps to the mineralocorticoid aldosterone. In the other layers of the cortex, progesterone is converted first to 17-hydroxyprogesterone and then to either the 17-hydroxysteroid cortisol or the 17-ketosteroid sex hormones. Each day the adrenal glands secrete 15–20 mg of cortisol, 25–30 mg of androgens, and 75–125 µg of aldosterone.
The mineralocorticoid aldosterone is produced in the outermost layer of the adrenal cortex, the zona glomerulosa. Aldosterone secretion is primarily controlled through a renal pathway. Decreased arterial pressure or decreased serum sodium concentration is sensed by the juxtaglomerular apparatus and the macula densa, respectively. The result is the production and release of renin, activating angiotensin I. Within the lung, angiotensin-converting enzyme (ACE) converts most of the angiotensin I to the angiotensin II. Circulating angiotensin II stimulates aldosterone secretion. To a lesser degree, aldosterone secretion is stimulated by direct effects of ACTH and elevated serum potassium. With aging, there is decreased production of aldosterone.
The zona fasciculata (ZF) and zona reticularis (ZR) are responsible for glucocorticoid production. Secretion of cortisol is controlled via the hypothalamic-pituitary-adrenal (HPA) axis. Hypothalamic corticotropin-releasing hormone (CRH) causes release of adrenocorticotrophic hormone (ACTH) from the anterior pituitary gland, which stimulates the adrenal cortex to release cortisol. As cortisol concentration achieves the physiologic range of 15–20 µg/dl, it exerts a negative feedback on both the hypothalamus and anterior pituitary secretion. ACTH has a plasma half-life of 25 minutes and cortisol has a plasma half-life of 90 minutes. ACTH and cortisol production is constant over life in normal, unstressed individuals. Adrenal androgen release is regulated by ACTH, whereas gonadal release of testosterone and estrogen are under a separate pathway of pituitary-gonadotrophic control. Androgen production peaks at puberty and progressively declines with advancing age.
Stimulation of the adrenal medulla is via preganglionic sympathetic fibers causing release of dopamine, norepinephrine and epinephrine. Sympathetic neural outflow is increased by the fight-or-flight response, fear, emotional stress, upright posture, pain, cold, hypotension, hypoglycemia and other stress. Norepinephrine exerts negative feedback at the preganglionic sympathetic receptors. With increasing age, there is no change in epinephrine levels, but norepinephrine and total plasma catecholamine are increased.
Read more about the Mini Back Scope Adrenalectomy (MBSA). This is the preferred adrenal operation for about 95% of people with an adrenal tumor.