How Your Kidneys Work
Most people know that the kidneys make urine, but not how. A simple way to begin to understand how is to think of a city's water treatment plant where all used water goes to be cleaned up so it can be used again and again. In a treatment plant, water is filtered so bad things are taken out and needed things are added. Think of the kidneys as a treatment plant for blood.
As blood flows in and out of your kidneys, it goes through thousands of tiny blood filters called glomeruli (glo-mer'u-li). The filters keep the good stuff in your blood and let the bad things out, such as extra water, chemicals and waste you don't need or that could be harmful if allowed to build up in your body. Fluid from the blood goes through filters and flows through tiny tubes connected to each filter. As fluid goes through the tubes, some things are removed and returned to the blood and some things are added to make the fluid become urine. All of the tubes in a kidney join a larger tube called the ureter. The ureter connects each kidney to the bladder, which is where the urine collects. When you are ready to get rid of the urine, it goes out through a tube called the urethra. The whole drainage system is called the urinary tract.
Normal healthy kidneys know how much urine to make depending on what your body needs. For instance, if you don't drink enough, your kidneys will make just enough urine to get rid of unneeded chemicals and waste, keeping you from getting dehydrated. If you drink more than you need, healthy kidneys will get rid of the extra fluid. However, if your kidneys don't work well, you could drink more than they can handle and the extra fluid would build up in your body. Problems occur when sick kidneys can't get rid of extra fluid, or when they cannot get rid of the extra chemicals or waste through your urine the way they are supposed to. Some sick kidneys lose too much water and chemicals too.
Two things kidneys remove from your blood are Blood Urea Nitrogen (BUN) from protein metabolism and creatinine from muscle metabolism. The doctor tests your blood for these things to see how well your kidneys are working. Normal creatinine depends on a person's size and ranges from 0.3 in a small infant to 1.5 in a large man. Pediatric kidney specialists are called Pediatric Nephrologists, and they will know the level of creatinine that is right for a child of a certain size. For example, if a normal creatinine for a child of specific size is 0.5 (100% working kidneys), a creatinine going up to 1.0 in that child would mean kidney function has decreased by one half, which is 50% kidney function. If the creatinine level keeps going up from 1.0 to 2.0, it means that kidney function has dropped another half, which is only 25% kidney function.
Kidneys do a lot of other things. They keep acids balanced in the body. They make vitamin D and help with calcium and phosphorus balance for healthy bones. Kidneys also make erythropoietin, a hormone that helps your body make blood. Another important thing kidneys do is help to regulate blood pressure. So if your kidneys don't work well, a lot of things can go wrong. Acid builds up in the body, bones suffer and can become deformed, anemia (low blood count) develops, blood pressure may get high, and if urine decreases, body fluids can build up. A waste product like BUN can get so high in the blood that it can cause nausea and cloudy thinking, even seizures or coma. Some kidneys let too many chemicals leak out into your urine. When this happens, tests are done to find out what the different chemicals are. The diagnosis and medicines needed to help slow the leak or replace the chemicals depend on what is leaking out. The problem may be permanent.