Normal bladder function

Filling and emptying your bladder is a complex interplay of kidney function, nerve signals and muscle activity. A problem anywhere in this system can contribute to overactive bladder and urge incontinence.

The kidneys produce urine, which drains into your bladder. When you urinate (void), the urine passes from your bladder through an opening at the bottom (neck) and flows out a tube called the urethra (u-REE-thruh). In women, the urethral opening is located just above the vagina. In men, the urethral opening is at the tip of the penis.

As your bladder fills, nerve signals alert your brain and eventually you'll feel the need to urinate. When you urinate, nerve signals coordinate the relaxation of the pelvic floor muscles and the muscles of the urethra (urinary sphincter muscles). The muscles of the bladder tighten (contract), pushing the urine out.

Involuntary bladder contractions

Symptoms of an overactive bladder occur because the muscles of the bladder are starting to contract involuntarily. This contraction creates the urgent need to urinate.

Several conditions may contribute to signs and symptoms of overactive bladder, including:

  • Neurological disorders, such as Parkinson's disease, strokes and multiple sclerosis
  • High urine production as might occur with high fluid intake, poor kidney function or diabetes
  • Medications that cause a rapid increase in urine production or require that you take them with lots of fluids
  • Acute urinary tract infections that can cause symptoms similar to an overactive bladder
  • Abnormalities in the bladder, such as tumors or bladder stones
  • Factors that obstruct bladder outflow — enlarged prostate, constipation or previous operations to treat other forms of incontinence
  • Excess consumption of caffeine or alcohol

Often, the specific cause of an overactive bladder isn't known.

Jan. 16, 2013

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