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Control of Urination

By

Patrick J. Shenot

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Apr 2020| Content last modified Apr 2020
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The kidneys constantly produce urine, which flows through two tubes (the ureters) to the bladder, where urine is stored (see Figure: Viewing the Urinary Tract Viewing the Urinary Tract The kidneys are bean-shaped organs that figure prominently in the urinary tract. Each is about 4 to 5 inches (12 centimeters) long and weighs about one third of a pound (150 grams). One lies... read more ). The lowest part of the bladder (the neck) is encircled by a muscle (the urinary sphincter) that remains contracted to close off the channel that carries urine out of the body (the urethra), so that urine is retained in the bladder until it is full.

When the bladder is full, messages travel along nerves from the bladder to the spinal cord. The messages are then relayed to the brain, and the person becomes aware of the urge to urinate. A person who has control of urination can consciously and voluntarily decide whether to release the urine from the bladder or to hold it for a while. When the decision is made to urinate, the sphincter muscle relaxes, allowing urine to flow out through the urethra, and the bladder wall muscles contract to push the urine out. Muscles in the abdominal wall and floor of the pelvis can be contracted voluntarily to increase the pressure on the bladder.

A variety of disorders can interfere with the control of urination, among them

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Test your knowledge

Urethritis
Urethritis is an infection of the urethra, the tube that transports urine out of the body from the bladder. Many organisms can cause urethritis. Which of the following is an organism that commonly causes urethritis in men, but is more likely to infect reproductive organs in women?  
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