The primary function of the kidney is to maintain a stable internal environment for optimal cell and tissue metabolism. These tasks are achieved by balancing solute and water transport, excretion of metabolic wastes, conserving nutrients and regulating acids and bases. The kidney also has an endocrine function by secreting the hormones renin, erythropoietin and 1,25-dihydroxyvitamin d3 for the regulation of blood pressure, red blood cell production and calcium metabolism respectively.