The Kidneys are one of the most important organs of the excretory system in human beings. The other organs are the liver, the lungs, and the digestive system. The kidneys filter blood and excrete the final products of metabolic activities and various other substances in body fluids including surplus water and electrolytes in urine. The kidney also produces hormones that are important for red blood cell formation (Erythropoietin), control of blood pressure (Renin) and calcium metabolism (1,25-dihydroxycholecalciferol, a form of active vitamin D3).