Each kidney contains millions of filter units called nephrons. The nephron consists of a glomerulus and a tubule. The glomerulus filters the blood of waste products, while retaining larger molecules that are required for the body to function properly. The filtered fluid then passes through the tubule, where salts, acids and water are regulated to keep the body in a normal metabolic state. After the filtered fluid passes through the tubule it is collected in the bladder as urine. Diseases, which affect the glomeruli or tubules result in kidney damage. Once kidney function is lost it is generally not recoverable and the only option for a patient's survival is dialysis or transplantation.