Diuretics are agents that increase the rate of urine formation. Although the definition is simple, a number of different physiological mechanisms are involved.

Diuretics are used to treat disorders such as hypertension and several types of edema that are caused by conditions such as heart failure and cirrhosis of the liver. However, use of diuretics can lead to complications, including dehydration and electrolyte imbalances.

The action of carbonic anhydrase inhibitors reduces the rate of hydrogen ion secretion and there reabsorption of bicarbonate ions. The bicarbonate ions increase tubular osmotic pressure, causing osmotic diuresis. With long-term use, the diuretic effects of carbonic anhydrase inhibitors tends to be lost. The diuretic effect of carbonic anhydrase inhibitors is useful in treating conditions such as glaucoma and altitude sickness.

Inhibitors of sodium ion reabsorption include thiazide-type diuretics. They promote the loss of sodium ions, chloride ions, and water in urine. These diuretics are given to some people who have hypertension. Inhibitors of sodium ion reabsorption, such as bumetanide, furosemide, and ethacrynic acid, specifically inhibit transport in the ascending limb of the loop of Henle. These diuretics are frequently used to treat congestive heart failure, cirrhosis of the liver, and renal disease.

Potassium-sparing diuretics are antagonists to aldosterone or directly prevent sodium ion reabsorption in the distal convoluted tubule and collecting duct. Thus they promote sodium ion and water loss in the urine. These diuretics are used to reduce the loss of potassium ions in the urine and therefore preserve or "spare" potassium ions. They are often used in combination with inhibitors of sodium ion reabsorption and are effective in preventing excess potassium loss in the urine.

Osmotic diuretics freely pass by filtration into the filtrate, and they undergo limited reabsorption by the nephron. These diuretics increase urine volume by elevating the osmotic concentration of the nephron, thus reducing the amount of water moving by osmosis out of the nephron. Urea, mannitol, and glycerine have been used as osmotic diuretics. Although they are not commonly used, they are effective in treating people who are suffering from cerebral edema and in treating edema in acute renal failure.

Xanthines, including caffeine and related substances, act as diuretics, partly because they increase renal blood flow and the rate of glomerular filtrate formation. They also influence the nephron by decreasing sodium and chloride reabsorption.

Alcohol acts as a diuretic, although it is not used clinically for that purpose. It inhibits ADH secretion from the posterior pituitary and results in increased urine volume.

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