The kidney (renes) weighs around 150-175 grams. It is placed behind the lowest rib, one on each side of the spine. The kidney's basic function is to clean the blood from waste of the body's metabolism, maintain the body's fluid-, salt-, acid- and base balance. All excess fluids becomes urin. There runs more then one liter of blood through the kidney pr. minute, and about 1700 liters in a day.