The way in which the kidneys work is pretty fascinating. These bean-shaped, fist-sized organs filter the blood in your body to remove wastes and to maintain proper levels of various substances in the blood. As one might imagine, the kidneys provide a valuable function in the body, ensuring that wastes do not accumulate, potentially causing health problems. As a result, a malfunctioning kidney is a cause for serious concern.

About 20% of the blood pumped out by the heart goes directly to the kidneys via the renal artery. Once the blood enters the kidneys, it is pumped up into the nephrons, tiny structures which filter the blood. Cleaned blood is sent out from the renal vein, returning to the heart for circulation to the rest of the body, while waste products drain to the bladder through the ureters. These organs are equipped to handle a very high volume of blood every 24 hours, and kidneys can even adapt to do the job independently, in the event that one kidney fails or is removed.

When blood enters a nephron, the nephron absorbs material which it thinks will be useful, allowing the rest to circulate through so that it reaches the ureter. The nephrons regulate the components of the blood, compensating for a large intake of salt, for example, or a reduced water intake. The goal of the kidneys is to keep the volume of water in the body constant while maintaining the composition of the blood by removing waste and keeping concentrations of various substances constant. In the process, the kidneys also keep the acid/base balance in the blood stable, regulate the body's blood pressure, maintain calcium, and stimulate the production of red blood cells.

The kidneys are quite efficient, extracting the maximum amount of value from the blood and producing surprisingly little waste. They work with the intestinal tract and the sweat glands to help remove wastes and toxins from the body, keeping the body healthy and in a state of homeostasis. However, kidneys can break down, causing serious health problems as toxins accumulate in the blood stream, rather than being filtered out. Kidney failure can happen to the elderly and to people with kidney diseases, and it requires prompt medical treatment, often including dialysis, a mechanical blood filtering treatment.

One sign that the kidneys are failing is blood in the urine, because normally kidneys do not filter red blood cells. Doctors can also test urine to look for specific proteins and other materials which can indicate unhealthy kidneys.