Describe the structure of the adrenal glands and the hormones that originate fro

The adrenal gland, or suprarenal gland, is a pyramid-shaped gland that sits on the superior border of each kidney.  Each adrenal gland has two parts: an outer adrenal cortex and an inner adrenal medulla.  

The Adrenal Cortex

The adrenal cortex produces more than two dozen steroid hormones, collectively called adrenocorticol steroids, or simply corticosteroids.  The adrenal cortex contains three distinct regions or zones.  Each zone synthesizes specific steroid hormones; the outer zone produces mineralocorticoids, the middle zone produces glucocorticoids, and the inner zone produces androgens.  

Mineralocorticoids (MCs): The minteralocorticoids affect the electrolyte composition of body fluids.  Aldosterone, the principal MC, stimulates the conversion of sodium ions and the elimination of potassium ions by targeting cells that regulate the ionic composition of excreted fluids.  Specifically, aldosterone causes the retention of sodium by preventing the loss of sodium ions in urine, sweat, saliva, and digestive secretions.  The retention of sodium ions is accopanied by a loss of potassium ions.  Secondarily, the reabsorption of sodium ions results in the osmotic reabsorption of water at the kidneys, sweat glands, salivary glands, and pancreas.  Aldosterone also increases the sensitivity of salt receptors in the tongue, resulting in greater interest in consuming salty foods.  Aldosterone secretion occurs in response to a drop in blood soium content, blood volume, or blood pressure, or to a rise in blood potassium levels.  Aldosterone release also occurs in response to the hormone angiotensin 2.  

Glucocorticoids (GCs): The steroid hormones collectively known as glucocorticoids affect glucose metabolism.  Cortisol (also called hydrocortisone), corticosterone, and cortisone are the three most important glucocorticoids.  These hormones accelerate the rates of glucose synthesis and glycogen formation, especially within the liver.  Simultaneously, adipose tissue responds by releasing fatty acids into the blood, and other tissues begin to break down fatty acids instead of glucose.  This glucose-sparing effect results in an increase in blood glucose levels.  Glucocorticoids also have anti-inflammatory effects; they suppress the activities of white blood cells and other components of the immune system.  "Steroid creams" are often used to control irritating allergic rashes, such as those produced by poison ivy, and injections of glucocorticoids may be used to control more severe allergic reactions.  Because they slow wound healing and suppress immune defenses against infectious organisms, topical steroids are used to treat superficial rashes but are never applied to open wounds.  

Androgens: The adrenal cortex in both sexes produces small quantities of androgens, the sex hormones produced in large quantities by the testes in males.  Once in the bloodstream, some of the androgens are converted to estrogens, the dominant sex hormone in females.  When secreted in normal amounts, neither androgens nor estrogens affect sexual characteristics, so the importance of the small adrenal production of androgens in both sexes remains unclear.  

The Adrenal Medulla

The adrenal medulla has a reddish brown coloration partly because of the many blood vessels within it.  It contains large, rounded cells similar to those found in other sympathetic ganglia, and these cells are innervated by preganglionic sympathetic fibers.  The secretory activities of the adrenal medullae are controlled by the sympathetic division of the autonomic nervous system (ANS).  The adrenal medulla contains two populations of secretory cells, one producing epinephrine (E, or adrenaline) and the other norepinephrine (NE, or noradrenaline).  These hormones are continuously released at a low rate, but sympathetic stimulation accelerates teh rate of discharge dramatically.  Epinephrine makes up 70-80 percent of the secretions from the medulla; the rest is norepinephrine.  Receptors for epinephrine and norepinephrine are found on skeletal muscle fibers, adipocytes, liver cells, and cardiac muscle fibers.  In skeletal muscles, adrenal medulla secretions trigger a mobilization of glycogen reserves and accelerate the breakdown of glucose to provide ATP; this combination results in increased muscular power and endurance.  In adipose tissue, stored fats are broken down to fatty acids, and in the liver, glycogen molecules are converted to glucose.  The fatty acids and glucose are then released into the circulation for use by peripheral tissues.  The heart responds to adrenal medulla hormones with an increase in the rate and force of cardiac contractions.  The metabolic changes that follow epinephrine and norepinephrine release peak 30 seconds after adrenal stimulation and linger for several minutes thereafter.  Thus, the effects produced by stimulation of the adrenal medullae outlast the other results of sympathetic activation.  

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Each adrenal gland consists of a cortex (outer region), which accounts for 80% of the adrenal gland, and an inner core called the medulla. These structures are essentially separate endocrine glands composed of different cell types that secrete different hormones. The cortex secretes a number of hormones that are collectively called adrenocorticoids, referring to their origin (cortex) and their structure (steroids). Three classes of adrenocorticoids are produced from within the adrenal cortex: mineralocorticoids, glucocorticoids, and sex hormones. Mineralocorticoids, such as aldosterone, are involved in regulating sodium and potassium secretion in the kidneys. Glucocorticoids, such as cortisol, are involved in regulating the body's response to stress by controlling carbohydrate, protein, and lipid metabolism as well as the availability of blood glucose. The sex hormones secreted by the adrenal cortex appear to play a minor role in the regulation of reproductive function as a consequence of the greater secretion of those hormones from the gonads. The cortex is stratified into three layers: zona glomerulosa, zona fasciculata, and zona reticularis. The zona glomerulosa is exclusively responsible for the production of mineralocorticoids, whereas the zona fasciculata and zona reticularis both play a role in the production of glucocorticoids and sex hormones. The adrenal medulla is one of the postganglionic cells of the sympathetic nervous system, containing chromaffin cells that secrete catecholamines. The secretion of the chromaffin cells contain 80% epinephrine, 20% norepinephrine, and a very small amount of dopamine.