The urinary system is a group of organs in the body that work together to filtrate and expel waste in the form of urine. The system is made up of the kidneys, ureters, bladder, and urethra. The kidneys are a pair of organs that sit on either side of the spine in the lower abdominal cavity. They are responsible for filtering blood and removing waste and excess fluid from the body in the form of urine. The ureters are a pair of tubes that connect the kidneys to the bladder. The bladder is a sac-like organ that stores urine until it is ready to be expelled from the body. The urethra is a tube that runs from the bladder to the outside of the body.