Health Tips for Diabetics description. What are Kidneys? The kidneys are 2 bean-shaped organs, each about the size of a fist. They are found in your back on either side of the spine. Kidneys are mainly responsible for filtering waste products, excess water, and other impurities out of the blood. These toxins are stored in the bladder and then removed during urination. The kidneys also regulate pH, salt, and potassium levels in the body. They produce hormones that regulate blood pressure and control the production of red blood cells. The kidneys even activate a form of vitamin D that helps the body absorb calcium.