The urinary system is responsible for nitrogenous waste excretion. The kidneys filter blood to remove urea and uric acid, which are produced as byproducts of protein breakdown in the liver. The nephrons are the functional units of the kidneys that filter blood and produce urine, which travels through the ureters and stores in the bladder before being excreted. Diseases of the urinary system can occur if there is a blockage or infection present.