The bladder is a hollow organ in the lower abdomen. It stores urine, the liquid waste produced by the kidneys. Urine passes from each kidney into the bladder through a tube called a ureter.

An outer layer of muscle surrounds the inner lining of the bladder. When the bladder is full, the muscles in the bladder wall can tighten to allow urination. Urine leaves the bladder through another tube, the urethra.

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