Both the liver and the kidneys are responsible for cleaning the blood. Both of these organs function as filters. However, while the liver operates as the body's main detoxifier, cleansing the blood of potential poisons, the kidneys work to eliminate waste and regulate the blood's chemical composition and maintain stability for optimum bodily function.
Technically part of the digestive system, the liver performs several functions as the body's main detoxifying organ, which includes acting as a filter for the blood and cleansing it of real and potential toxins. The liver both eliminates harmful substances produced during normal functions, such as breaking down proteins through digestion, as well as locates and tries to break down and clear out harmful substances that the body ingests, including alcohol, caffeine and some prescription drugs. Nearly all of the blood in the body passes through the liver's filtration system at some point.
The kidneys, on the other hand, work to regulate the blood's chemistry independent of these toxic substances. They do this through units inside each kidney called nephrons, which filter out waste and cast it out as urine while returning vital minerals back into the blood stream. All of the body's blood passes through this process, and in doing so, the kidneys regulate everything from fluid volume to electrolyte levels to the hormones responsible for regulating blood pressure and producing red blood cells.