The function of the bladder is mainly to store and expel urine, just like a balloon, which is flexible and stores urine temporarily and then expels it when appropriate. A normal adult bladder can store about 400 to 500 ml of urine. It is related to the amount of water intake per day and urinates about 4 to 8 times per day. When the bladder storage is nearly full, the nervous system will send a signal to the brain “I want to urinate”, and the brain tells us that it is time to go to the bathroom. In fact, at this time, normal people can still hold back for a while. When the bathroom is found, the bladder will contract to expel the urine.