Anatomy and Physiology of the Bladder System

Bladder control means more than just telling yourself to wait to urinate until you get to the bathroom. It is not that simple. It takes teamwork from many organs, muscles, and nerves in your body. 

Most of the bladder control system is inside your pelvis, the area of your abdomen between your hips and below the belly button. Your bladder is a muscle shaped like a balloon. When the bladder stores urine, the bladder muscle relaxes. When you urinate, the bladder muscle tightens to squeeze urine out of the bladder.

More muscles help with bladder control. Two sphincter muscles surround the tube that carries urine from your bladder down to an opening in the front of the vagina. The tube is called the urethra. Urine leaves your body through this tube. The sphincter muscles keep the urethra closed by squeezing like rubber bands.

Pelvic floor muscles support the uterus, or womb, and rectum and bladder. They also help keep the urethra closed.

When the bladder is full, nerves in your bladder signal the brain. That's when you get the urge to urinate. Once you reach the toilet, your brain sends a message down to the sphincter muscles and the pelvic floor muscles. The brain tells them to relax. The brain also tells the bladder muscles to tighten up to squeeze urine out of the bladder.

Loss of bladder control in women most often happens because of problems with the muscles that help to hold or release urine: the bladder muscle, the sphincter muscles, and the pelvic floor muscles. Incontinence occurs if your bladder muscles suddenly contract (or squeeze) or if the muscles around the urethra suddenly relax.