Bladder is one of the six fu organs, which is located in the center of the front part of the lower abdomen and is cystic. Its main function is to store water and excrete urine through gasification. In mammals, it is a cystic structure composed of smooth muscle, located in the pelvis, and its posterior opening communicates with the urethra. There is a sphincter at the junction of bladder and urethra, which can control the discharge of urine.