Female bladder. Artwork showing a section through the female urinary system. The bladder is seen as a pink sac at centre. This is a hollow organ that holds urine. Two tubes (ureters) from upper image lead urine from the kidneys to the bladder. Yellow drops of urine are seen emerging from the trigone, the triangular space at the base of the bladder (lower centre). At the base of the bladder, the narrow urethra emerges, a tube that carries urine to the exterior opening. Just above the exterior opening, pink muscles of the urethral sphincter are seen. This muscle relaxes or contracts to control the flow of urine out of the bladder.