The bladder is a hollow muscular organ that is located in the pelvis. The bladder has two functions: one is to store urine and the other is to release/expel urine. Urine drains from the kidneys (one on each side of the body), down the ureters (one on each side of the body), and into the bladder. The urine is stored in the bladder where it remains until urination.
When it is time to urinate, the bladder muscle contracts and the outlet of the bladder and sphincter muscles relax to allow urine to pass through the urethra to leave the body.The bladder and urethra are part of the lower urinary tract, whereas the kidneys and ureters are part of the upper urinary tract. The\ urine in the bladder is normally free of bacteria (sterile). However, bacteria may be present in the bladder but not cause inflammation or symptoms of an infection.