In this way, your kidneys regulate the body's level of these substances. The right balance is necessary for life, but excess levels can be harmful. In the nephron (left), tiny blood vessels intertwine with urine-collecting tubes. Each kidney contains about 1 million nephrons. In addition to removing wastes, your kidneys release three important hormones: 1  Erythropoietin (eh-RITH-ro-POYeh-tin), or EPO, which stimulates the bones to make red blood cells. 2  Renin (REE-nin), which regulates blood pressure.