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Diuretics: FAQs

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What are diuretics and how do they work?

The amount of fluid (water) retained by the body is controlled primarily by the kidneys. This occurs due to the kidney's ability to control the retention and elimination of sodium and chloride, because the amounts of sodium, chloride, and water in the body are carefully balanced. Thus, if sodium and chloride are eliminated from the body, water also is eliminated. Conversely, if sodium and chloride are retained by the body, so is water.

The elimination of sodium, chloride, and water from the body is somewhat complex. In the kidneys, sodium, chloride, and other small molecules are filtered out of the blood and into the tubules of the kidney where urine is formed. Most of the sodium, chloride, and water are reabsorbed into the blood before the filtered fluid leaves the kidney in the form of urine. To make matters even more complex, there are different mechanisms that are active in different parts of the tubules that affect the reabsorption of sodium and chloride.

Diuretics are a class of drugs that increase the flow of urine (termed diuresis). Diuretics work by removing sodium and chloride from the body in the urine, and the sodium and chloride in turn draw excess water from the body. The amount of sodium and chloride (sodium chloride, or NaCl) in the body, as previously discussed, has a marked effect on the amount of water retained by the body; hence most diuretics have their effects by reducing total-body sodium chloride content.

It is important to note that there is a delicate balance between dietary sodium intake and sodium loss. If the balance is compromised and there is a greater intake of sodium into the body but not enough removal of sodium, complications of fluid overload may occur, such as edema, pulmonary edema, or high blood pressure. When there is greater removal of sodium, but not enough intake of sodium, complications of fluid depletion may occur such as renal failure or reduced output of blood from the heart.

Continued use of diuretics, will cause some overall sodium and chloride loss. The body, however, has a natural way of compensating for these losses by reducing the excretion of sodium and chloride and stabilizing the amount of sodium, chloride and water in the body. In this manner, fluid depletion usually is prevented.




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