The bladder is a tissue organ of the body, and both men and women have this organ. It is located within the pelvic cavity of the lower abdomen and lies completely within the pelvic cavity in a void state; when filled with a certain amount of urine, it can rise above the pelvic cavity. The bladder is lined with a smooth mucosa, with a thick muscle layer in the middle and fatty tissue around the periphery to protect the bladder. The posterior wall of the bladder has openings for the ureters on both sides, and the front of the bladder is connected to the urethra, whose function is to collect the urine left after filtration by the kidneys and to store it. When the bladder fills to a certain level, it gives a signal to the brain to urinate. At this point, the brain releases the signal to urinate, causing the muscles of the bladder to contract, the posterior urethral sphincter to open, and urine to be expelled from the body.