Here’s how your cat’s urinary system works. The kidneys filter waste and toxins from the blood. These waste products then become part of the urine in the kidneys. Urine leaves the kidneys through narrow tubes called ureters, which empty into the bladder. When your cat urinates, the bladder is emptied through a tube called the urethra. Feline urinary problems are usually grouped into conditions of the lower urinary tract (the bladder and urethra) and the upper urinary tract (the kidneys and ureters).