The excretory system removes waste from the body through various organs including the lungs, skin, colon and kidneys. The kidneys filter the blood and produce urine, which contains water and waste products like urea and uric acid. The urine travels from the kidneys to the bladder through the ureters for storage, and is then excreted from the body through the urethra. Diseases of the excretory system can include kidney stones, cystitis, and renal insufficiency if the kidneys fail to correctly filter waste from the blood.