How Does the Bladder Work?

Your bladder is a hollow muscular organ that’s shaped like a balloon. It sits in your pelvis and is held in place by ligaments attached to other organs and the pelvic bones. Your bladder stores urine until you are ready to go to the bathroom to empty it. It will swell into a round shape when full, then deflate when empty. In a healthy urinary system, the bladder can comfortably hold up to 16 ounces (2 cups) of urine for 2 to 5 hours.

Circular muscles called sphincters help keep urine from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the urethra, which is the tube that allows urine to pass outside the body.

Nerves in the bladder tell you when it is time to urinate, or go to the bathroom. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The sensation to urinate becomes stronger as the bladder continues to fill and reaches its limit. At that point, nerves from the bladder send messages to the brain that your bladder is full, and the urge to empty your bladder intensifies.

When you urinate, the brain signals the bladder muscles to tighten, squeezing urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax. As these muscles relax, urine exits the bladder through the urethra. Normal urination happens when all these signals occur in the correct order.