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Monday, May 20, 2013
Urinary incontinence occurs when the urinary system can't properly control the storage of urine in the bladder and its periodic release. An adult who becomes incontinent will involuntarily release urine before finding a toilet, and sometimes even before knowing the bladder is emptying.
To gain a better understanding of urinary incontinence, let's start with a basic description of how the urinary system is supposed to work. While there is some variation of the male and female urinary tract, the basic process of filling, storing and emptying the bladder of urine is handled the same way in both sexes.
The purpose of the lower urinary system is to accumulate, store and eventually release urine from the body. Urine is water and liquid waste that's been filtered out of the bloodstream by the kidneys. From here, it's sent to the bladder and temporarily stored.
The bladder is an elastic container located in the pelvis. It stretches like a balloon and can normally hold more than two cups of urine. The bladder is surrounded by a layer of muscle known as the detrusor muscle. At the base-or the neck-of the bladder is a tube-like opening which is called the urethra. This is a drainage tube that takes the urine out of the body upon urination.
Sphincter muscles, which line the wall of the urethra and the base of the bladder, seal the bladder most of the time so the urine doesn't leak out unexpectedly. The sphincter grasps the neck of the bladder much like a tightened string keeps air from leaking from a balloon. As the bladder fills, nerve endings in the bladder send an electrical signal that travels through the central nervous system to the brain, alerting it that the bladder should be emptied soon. The individual usually has plenty of warning after getting that brain signal.
When the decision is made to empty the bladder, the sphincter muscles relax, opening the passage like the string being loosened from the balloon. At the same time, the detrusor muscle that forms the bladder wall squeezes the urine out of the bladder, down the urethra and out of the body. When the bladder is emptied, the sphincter contracts, once again sealing the base of the bladder, and the detrusor muscle relaxes.
That's how the system is supposed to work, and usually does. But when some part of this system malfunctions, incontinence can occur. Here's what can go wrong:
An overactive bladder contracts involuntarily. This often results in urge incontinence, the most common form of incontinence. It means that the bladder contracts, sending urine down the urethra, even when you don't want it to, and well before the bladder is filled. The causes can include infection in the bladder lining and malfunctioning of the nerves that send the signal to the brain that urination is needed.
A weak or damaged sphincter or abnormality of the urethra can lead to stress incontinence, which you can think of as being caused by a leaky system. The urine seeps out of the bladder with any sudden stress on the abdomen, such as a sneeze, cough, laughter or exercise. Imagine a balloon that hasn't been tightly knotted or whose fabric is leaky or damaged.
Bladder weakness or blockage leads to overflow. This is called overflow incontinence. It's when some kind of blockage or bladder weakness postpones urination until the point where the need can no longer be ignored. Since a common cause of such a blockage is an enlarged prostate pressing against the urethra, overflow incontinence is primarily seen in men. Bladder weakness can be caused by a variety of factors including diabetes and heavy alcohol use, among others.
This article is a NetWellness exclusive.
Last Reviewed: May 14, 2007
Martin I Resnick, MD
Formerly, Professor of Urology
School of Medicine
Case Western Reserve University