Category B - full version without watermark 720x576 (check terms and conditions at The embed version with watermark is free of charge. Text: Kidneys with their manifold functions. The kidney is among other things a detoxification organ. On the one hand it excretes the body's own metabolic waste products on the other hand it detoxifies the body from foreign substances like drugs. For that purpose the kidneys dispose of 2 million filter cells, at the top left you can see one of those renal corpuscles. How is urine produced? Blood streams through the filter cell, leading to the so called primary urine which is further processed within a complicated tube system. About 179 l from the 180l of primary urine are resorbed by the cells of the tube system. The reminder of about one liter is then the urine which will be excreted.