How does your Bladder work?

The Urinary System

Your urinary system consists of two kidneys, two ureters, one bladder and one urethra. Most people have two kidneys but you can function healthily with one.

Urine Flow and Control

Step 1: Storing urine
Every time you eat and drink, your body absorbs liquids. The kidneys filter out waste products from the blood and make urine. Urine flows downward from the kidneys to the bladder through a pair of tubes called ureters.

The bladder is a balloon-like organ that changes shape according to the amount of urine it contains. It looks like a deflated balloon when it is empty and then becomes somewhat pear-shaped when the amount of urine inside increases.

Step 2: Releasing urine
Urine leaves the bladder and exits the body through a tube called the urethra.
The process of emptying the bladder - urination - is sometimes also called "voiding". Urination is controlled by muscles, called sphincters, which surround the urethra. The sphincters keep the urethra closed by squeezing like tight rubber bands.

Pelvic floor muscles under the bladder also help keep the urethra closed. Urine stays inside the body when the sphincter and pelvic floor muscles are tight. When the bladder is full, nerves in your bladder signal the brain. That's when you get the urge to go to the bathroom.

Once you reach a toilet, your brain sends a message to the large bladder muscle - called the detrusor - to contract so that it squeezes urine out of the bladder. At the same time, the brain tells the sphincter and pelvic floor muscles to relax and let the urine through. When you are finished urinating, the sphincters once again contract, and the bladder muscles stops squeezing and relaxes.

Knowing how a healthy bladder works will help you understand what happens when bladder control is a problem.