Your kidneys play a vital role in regulating your blood composition. Inside your body, the water, acid levels (pH) and salt levels need to be kept constant and your kidneys play a part in this by filtering huge volumes of blood as it passes round the body.
Blood is carried into the kidneys by the renal artery. You will have around one to one and a half gallons of blood circulating through your body and your kidneys filter that blood as many as 400 times a day. The blood enters your kidney and is distributed to tiny filtration units known as nephrons. These nephrons filter substances like water, salts, acids and alkalis out of your blood and then reabsorb some of them. It is this secretion or reabsorbtion that keeps your blood composition constant.
Excess water and waste products are then secreted as urine. Urine passes from the kidney, though a tube called the ureter, to the bladder. The amount of urine is constantly managed by your kidneys to maintain your blood composition. If you don't have enough fluid in your body, the brain communicates with the kidneys by sending out a hormone that tells the kidneys to hold on to some fluids. When you drink more, this hormone level goes down, and the kidneys will release more.
When kidneys go wrong
People can live healthily with one functioning kidney. However, when about 90% of kidney function has been lost, a person can only survive by having dialysis. Dialysis works by using a machine that replicates the blood-cleaning function of healthy kidneys. In the most extreme cases of kidney failure, survival depends on the person receiving a donor organ.
Diabetes mellitus, a condition causing high blood sugar levels, is the most common cause of kidney transplantation. Other causes include high blood pressure and some infections.
Your kidney's other functions
In addition to balancing the volume of fluids and minerals in the body (a principle called homeostasis), your kidneys have other functions. They constantly react to hormones that the brain and other organs sends them. For example, when your kidneys detect that your blood pressure is dropping, they secrete an enzyme called renin. This enzyme triggers a chain of events that makes your kidneys reabsorb more salt and water, leading to an increase in blood pressure.
Your kidneys even make some of their own hormones. For example, the kidneys produce a hormone that tells the body to make red blood cells.