The human kidney filters about a cup of blood every minute, removing waste, excess fluid, and toxins from it, while also regulating blood pressure, balancing important electrolytes, activating Vitamin D, and helping the body produce red blood cells. This broad range of functions is achieved in part via the kidney's complex organization. In its outer region, more than a million microscopic units, known as nephrons, filter blood, reabsorb necessary nutrients, and secrete waste in the form of urine.