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The suprarenal glands are located on top of each of the kidneys. The adrenal cortex (outer portions) produce the corticosteroids: the mineralcorticoids and the glucocorticoids which are steroid hormones. The cortex also produces some male sex steroids. Cholesterol is the starting place for the biosynthesis of all these steroid hormones.
The adrenal medulla is actually an extension of the nervous system. The adrenal medulla produces norepinephrine and epinepherine (adrenaline) that are released in response to stress or a fright.
Mineralcorticoids
The major mineralcorticoid, which is secreted almost independently of ACTH from the pitutitary, is aldosterone. Aldosterone secretion is controlled mostly by the levels of potassium and sodium in serum and a blood pressure control system called the renin-angiotensin system. The principle action of aldosterone is the retention of sodium. Where sodium goes, so goes associated ions and water. Therefore, aldosterone profoundly effects fluid balance by effecting intracellular and extracellular fluid volume.
Aldosterone has the opposite effect on serum levels of potassium as it is lost in the urine in exchange for sodium in the renal tubules. Salivary and sweat glands are also influenced by aldosterone to save sodium and the intestine increases the absorption of sodium in response to aldosterone.
Aldosterone levels increase and cause fluid retention in diseases such as congestive heart failure and liver cirrhosis. Certain diuretics act by antagonizing aldosterone. In contrast to most diuretics that cause potassium loss, the aldosterone antagonists increase blood potassium and are sometimes used for this effect.
Glucocorticoids
The major glucocorticoid is cortisol. Cortisol has important actions in the control and metabolism of carbohydrates, lipids, and proteins and assists in the metabolic reaction to stress, especially chronic stress. It causes glucose to be liberated from the liver by increasing glucose production from fatty acids (by-products of lipid breakdown) and amino acids. Cortisol causes the tissues to take up less glucose from the blood and mobilizes fat breakdown. The net effect is to increase serum glucose concentrations which is protective for the brain in that it cannot use any other fuel source than glucose. It also stimulates protein breakdown for glucose formation in all tissues except the liver where it stimulates protein synthesis.
At high concentrations (greater than physiologic) glucocorticoids (such as hydrocortisone or prednisone) are useful for the treatment of allergies and inflammation. Each step of the inflammatory process is blocked by glucocorticoids when given systemically (an IV injection or orally). Topical application of glucocorticoids have anti-inflammatory effects for the local area. The anti-inflammatory activity of glucocorticoids is thought to be due primarily to the stabilization of cell membranes and the inhibition of phospholipases and therefore prostaglandin synthesis. The immune response can also be suppressed by the use of glucocorticoids. Eosinophils and lymphocytes decrease in the circulation affecting both cellular and humoral immunity. The glucocorticoids are used for many other conditions including asthma, renal diseases, rheumatic disorders such as lupus and inflammatory bowel disease.
The adrenal medulla is actually an extension of the nervous system. The adrenal medulla produces norepinephrine and epinepherine (adrenaline) that are released in response to stress or a fright.
Mineralcorticoids
The major mineralcorticoid, which is secreted almost independently of ACTH from the pitutitary, is aldosterone. Aldosterone secretion is controlled mostly by the levels of potassium and sodium in serum and a blood pressure control system called the renin-angiotensin system. The principle action of aldosterone is the retention of sodium. Where sodium goes, so goes associated ions and water. Therefore, aldosterone profoundly effects fluid balance by effecting intracellular and extracellular fluid volume.
Aldosterone has the opposite effect on serum levels of potassium as it is lost in the urine in exchange for sodium in the renal tubules. Salivary and sweat glands are also influenced by aldosterone to save sodium and the intestine increases the absorption of sodium in response to aldosterone.
Aldosterone levels increase and cause fluid retention in diseases such as congestive heart failure and liver cirrhosis. Certain diuretics act by antagonizing aldosterone. In contrast to most diuretics that cause potassium loss, the aldosterone antagonists increase blood potassium and are sometimes used for this effect.
Glucocorticoids
The major glucocorticoid is cortisol. Cortisol has important actions in the control and metabolism of carbohydrates, lipids, and proteins and assists in the metabolic reaction to stress, especially chronic stress. It causes glucose to be liberated from the liver by increasing glucose production from fatty acids (by-products of lipid breakdown) and amino acids. Cortisol causes the tissues to take up less glucose from the blood and mobilizes fat breakdown. The net effect is to increase serum glucose concentrations which is protective for the brain in that it cannot use any other fuel source than glucose. It also stimulates protein breakdown for glucose formation in all tissues except the liver where it stimulates protein synthesis.
At high concentrations (greater than physiologic) glucocorticoids (such as hydrocortisone or prednisone) are useful for the treatment of allergies and inflammation. Each step of the inflammatory process is blocked by glucocorticoids when given systemically (an IV injection or orally). Topical application of glucocorticoids have anti-inflammatory effects for the local area. The anti-inflammatory activity of glucocorticoids is thought to be due primarily to the stabilization of cell membranes and the inhibition of phospholipases and therefore prostaglandin synthesis. The immune response can also be suppressed by the use of glucocorticoids. Eosinophils and lymphocytes decrease in the circulation affecting both cellular and humoral immunity. The glucocorticoids are used for many other conditions including asthma, renal diseases, rheumatic disorders such as lupus and inflammatory bowel disease.
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