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Duretics
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We all know what they do - but how exactly do they work ?
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Your kidneys have a network of tubes that make urine by filtering your blood in two stages. In the first stage, water, salt and waste products such as urea are filtered out from your blood, leaving behind red and white blood cells. A lot of nutrients and other essential substances also leave your blood at this stage.
In the second stage, your kidneys re-absorb these nutrients and essential substances back into the blood. This leaves waste products, plus some salt and water (urine) in your kidneys. The urine travels down tubes to your bladder where it's stored until you go to the toilet.
Heart failure can make your kidneys re-absorb more water and salt into the blood, and so produce less urine. This is your body's way of trying to compensate for the reduced pumping power of the heart, but it can make matters worse. There is a greater volume of blood for your heart to pump, and so more work for it to do. Also, excess water in the blood can leak out into your lungs, making you feel breathless (pulmonary oedema) and into the legs causing your ankles and feet to swell up (peripheral oedema).
In the second stage, your kidneys re-absorb these nutrients and essential substances back into the blood. This leaves waste products, plus some salt and water (urine) in your kidneys. The urine travels down tubes to your bladder where it's stored until you go to the toilet.
Heart failure can make your kidneys re-absorb more water and salt into the blood, and so produce less urine. This is your body's way of trying to compensate for the reduced pumping power of the heart, but it can make matters worse. There is a greater volume of blood for your heart to pump, and so more work for it to do. Also, excess water in the blood can leak out into your lungs, making you feel breathless (pulmonary oedema) and into the legs causing your ankles and feet to swell up (peripheral oedema).
Diuretics reduce the amount of water and salt that is re-absorbed by your kidneys. So, more water and salt passes out with the waste products into your urine. This means that you make more urine and so lose more water from your blood. The overall volume of blood is reduced, which gives your heart less work to do and helps to reduce your blood pressure. This is why diuretics are used to treat heart failure and high blood pressure.
I still don't think anyone has answered your question yet.
Reabsorption of fluids from the kidney tubules is controlled by the anti-diuretic hormone (ADH) secreted by the dorsal pituitary gland.
Anything that blocks either the production, or the action of ADH will therefore prevent this reabsorption and the fluid will pass to the bladder to be excreted.
Tea and alcoholic drinks suppress the production of this hormone and so increase urine production by failing to reabsorb it.
Different drugs may act in one of three ways:
a) They may also inhibit ADH production
or b) They may bind to the hormone molecules and therefore block its action.
or c) the drug may bind to the receptor sites in the kidney preventing the hormone from 'docking'.
Reabsorption of fluids from the kidney tubules is controlled by the anti-diuretic hormone (ADH) secreted by the dorsal pituitary gland.
Anything that blocks either the production, or the action of ADH will therefore prevent this reabsorption and the fluid will pass to the bladder to be excreted.
Tea and alcoholic drinks suppress the production of this hormone and so increase urine production by failing to reabsorb it.
Different drugs may act in one of three ways:
a) They may also inhibit ADH production
or b) They may bind to the hormone molecules and therefore block its action.
or c) the drug may bind to the receptor sites in the kidney preventing the hormone from 'docking'.
//Your kidneys have a network of tubes that make urine by filtering your blood in two stages. In the first stage, water, salt and waste products such as urea are filtered out from your blood, leaving behind red and white blood cells. A lot of nutrients and other essential substances also leave your blood at this stage. //
Why does the kidneys filter out these products - only to re-absorbed them again ?
Why does the kidneys filter out these products - only to re-absorbed them again ?
Not everything is reabsorbed, only enough to maintain a balance. the kidneys are amazing filtering organs. In severe kidney failure nothing may be excreted resulting in a very ill person. Many drugs/medicines are excreted by the kidneys, if they were not, toxic levels would build up in the body (because you are taking the next dose and so on) and again you would be very ill. Diuretics effect the amount of water and salt excreted, and not reabsorbed in the second stage; salt is the main thing excreted - water follows the salt, because it is attracted to it. Too much salt loss causes problems too, and needs careful monitoring. If you do not have hypertension or heart problems, then your kidneys are just a processing factory for waste fluid product and does not need help from diuretics; if you do have these problems, then diuretics are extremely helpful. Another example; some very poisonous mushrooms 'kill' the body in this way. The toxins are not filtered out, instead they are reabsorbed, re-circulated through the liver and back again to the kidneys causing more damage/failure of the kidney and liver on each circuit.
//Why does the kidneys filter out these products - only to re-absorbed them again? //
If you think about it, it makes sense. That way your body doesn't have to recognise all the millions of potential chemicals that it needs to get rid of, it only has to recognise the much smaller number of ones it needs. Try this analogy:- what is the best way of clearing out a drawer? - Yes, empty the whole lot out and just put back the few items that you need to keep. Everything else can be discarded (excreted).
If you think about it, it makes sense. That way your body doesn't have to recognise all the millions of potential chemicals that it needs to get rid of, it only has to recognise the much smaller number of ones it needs. Try this analogy:- what is the best way of clearing out a drawer? - Yes, empty the whole lot out and just put back the few items that you need to keep. Everything else can be discarded (excreted).
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