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Control of Urination


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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Tubulointerstitial Nephritis
The kidneys contain tubules, which are structures in the kidneys that are involved in filtering fluids. Tubulointerstitial nephritis is inflammation that affects the tubules and the tissue surrounding them, called “interstitial tissue.” Onset of tubulointerstitial nephritis may be acute (sudden) or chronic (gradual) and often results in kidney failure. Which of the following is the most common cause of acute tubulointerstitial nephritis?
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