How we normally pass urine...

The kidneys produce urine, and this collects in the bladder, which is a muscular bag found in the middle of the pelvis low in the abdomen, behind the pubic bone. As the urine enters the bladder drip by drip, the bladder expands like a balloon as more urine is collected.

The amount of urine produced by the kidneys depends on many factors including how much you drink, how much you sweat and how much you eat.

You would start to be aware of a filling bladder when it holds about 280ml of urine. When full, (a full bladder contains about 350ml of urine) the bladder sends nerve impulses to your brain that it needs to empty, and then in a healthy system despite the signals to empty, the brain can control the opening mechanism of the bladder for a few minutes until a convenient time (when you find a toilet).

When appropriate, the brain tells the muscular walls of the bladder via nerve impulses to contract at the same time as a valve (sphincter) relaxes at the entrance to the urethra, which is a tube through which the urine flows to the outside world. The bladder is emptied at our control.

The muscles below the bladder that surround the urethra are called ‘pelvic floor muscles' and are important in holding the bladder and urethra in place. If these muscles are weakened (for example by pregnancy or childbirth) it can make it difficult to hold the urge to pass urine and leakages occur.

Most incontinence stems from a problem with one or more of these processes involving the muscles nerves and sphincter.