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.
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 muscle (also known as the detrusor muscle) that changes shape according to the amount of urine it contains. It collects and stores urine that is produced by the kidneys, it can hold around 500mls or 1 pint. 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
As the bladder fills towards capacity, a nerve signal is sent from the bladder to the brain giving a sensation that it needs to pass urine. By tightening your pelvic floor and urethral sphincter muscles you should be able to delay the urge and postpone emptying the bladder until it is convenient at the right time and place.
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.
It is normal to empty your bladder 8 times in a 24 hour period.
Knowing how a healthy bladder works will help you understand what happens when bladder control is a problem.