The urinary bladder is an organ. It stores urine. It is part of the urinary system. All the liquids that are drunk go through the bladder. The bladder takes in the liquid in order for the body to work. The bladder works with the kidneys. The kidneys clean the liquid. This goes on until the bladder is too full to hold any more. At this point, it is about the size of a softball. The bladder then tells the brain that it needs to be emptied. When this message is received by the brain, the muscles around the bladder start to squeeze and the bladder starts to contract. At the same time, the bladder sends a message to the sphincters to relax and let the liquid pass through the urethra out of the body.

All species of mammal have a urinary bladder.^[1]

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  The inside of the bladder

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  Human male and female urinary bladders and urethras

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  (Nearby location) Bladder location and associated structures in the male

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  Animals

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  Bladder, prostate, and seminal vesicles of a stallion (horse)