The excretory system, is composed of multiple organs.  The primary organ is the kidney.  The kidney performs the dual tasks of filtering out wastes and purifying blood.  Other organs in the  excretory system include; the urinary bladder, the ureters, and the urethra. The urinary bladder is a large hollow muscular sac that holds urine.  The ureters are two tubes that transport urine from the kidneys to the urinary bladder.  The urethra is a tube that transports urine from the bladder to an opening outside the body.