The bladder is a hollow organ in the lower abdomen (pelvis). It collects and stores urine produced by the kidneys.
The bladder is connected to the kidneys by a tube from each kidney called a ureter.
When the bladder reaches its capacity of urine, the bladder wall contracts, although adults have voluntary control over the timing of this contraction. At the same time, a urinary control muscle (sphincter) in the urethra relaxes. The urine is then expelled from the bladder.
The urine flows through a narrow tube called the urethra and leaves the body. This process is called urination, or micturition.