Craig C. Freudenrich
Sometimes, a person's body retains too much fluid. Diuretics are a class of medications designed to help control fluid retention and to treat several conditions, especially high blood pressure. They also help people who have congestive heart failure, liver cirrhosis, kidney disease and edema, or fluid retention from any number of causes.
Your kidneys work by filtering the fluid and small substances in your blood. They then reabsorb salts, such as sodium and chloride, along with glucose and water, from the filtrate. Materials that are filtered, but not reabsorbed, are excreted in your urine. The reabsorbing of sodium and water are linked. The more sodium that gets reabsorbed, the more water gets reabsorbed. So, if a lot of water and sodium are reabsorbed, then the circulating blood volume increases. This keeps blood pressure high. In contrast, if the kidneys reabsorb less sodium and water and the circulating blood volume is reduced, this in turn reduces blood pressure.
Diuretics act directly on the cells of the kidney that reabsorb sodium. They inhibit the transport proteins that move sodium ions from the filtrate into the cells and then into the blood. This means that the kidneys reabsorb less sodium and water. High blood pressure depends upon the force of the heart's contractions, the degree of constriction of the blood vessels and the volume of blood circulating in your body. Your kidneys help control the volume of circulating blood. When diuretics help make sure that the body has less circulating blood volume, they help lower blood pressure. This action of diuretics increases the excretion of sodium and water in the urine. Diuretics often are referred to as "water pills." The increased urine flow makes the patient go to the restroom more, which is an unpleasant side effect of the medication.
There are three classes of diuretics:
- Thiazide diuretics -- hydrochlorothiazide, metolazone and chlorothiazide
- Loop diuretics -- bumetanide, furosemide, ethacrynic acid and torsemide
- Potassium-sparing diuretics -- spironolactone, triamterine and amilioride
The various classes act on different parts of the kidneys.(John Foxx/Getty Images)
The purpose of diuretics is to help your body get rid of sodium and water in order to reduce the volume of fluids passing through your arteries. That's why some people call them "water pills." The way that diuretics work is they force your kidneys to expel salt into your urine. When kidneys release the salt, they also release water from your blood along with it. Having less water in your blood means your blood takes up less space, which is important for someone who needs to minimize the pressure on his or her arteries.
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