We can’t live without our kidneys. Luckily, we are born with two, and if one goes on an extended vacation the other can step up and do the job, but without both, we’re toast. The kidneys are responsible for filtering our blood and getting rid of all the harmful waste materials from the many daily processes our cells undergo. Urine is essentially filtered blood. When you drink fluid containing water, the water adds to your blood volume and your kidney adjusts how much is filtered to maintain a consistent blood pressure. That is why drinking a lot makes you go to the bathroom. Also, it’s why dehydration is so bad for you. Your body needs to get rid of waste in the blood, but it can’t continue taking from the blood volume without anything to replace it (water).
Now that we know what the main function of the kidneys are, it should come as no surprise how we determine if they are functioning properly: by testing for blood levels of substances the kidneys are supposed to filter out. Two of those are creatinine and blood urea nitrogen (BUN). When the kidney first filters the blood, it takes a large chunk of it and then the body selectively chooses what to reabsorb based on needs. It’s kind of like dumbing a huge box of old junk onto the floor and then going through to see what you want to keep and what you want to throw away. Creatinine is the waste product of creatine phosphate in muscles and is almost never chosen for reabsorption. If blood levels get high, that means the kidneys aren’t doing their jobs. BUN, however, is regularly reabsorbed but high blood levels can still tell us a story. It means the kidney isn’t filtering out as much blood as it should, which is a result of dehydration or low blood pressure.
The kidneys are closely tied to the heart and can heavily regulate blood pressure, so bad kidneys can lead to hypertension. They do this by regulating the absorption of electrolytes, or telling blood vessels to squeeze tighter. It’s important to ensure the proper functioning of this organ to a long, happy life.