The location of the kidney: behind the abdomen, to the left and right of the spine. A human being generally has two kidneys, but there are those who have only one, but this organ functions well. The function of the kidneys: filter the elements transported by the blood, balance the water needs, preserve the minerals necessary for the organism, balance the acid necessary for the organism, produce hormones. Symptoms of kidney disease: bloody urine, micturition, feeling tired, abdominal or back pain, joint pain, frequent urination