Urinary Retention (cont.)
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What is the urinary tract?
The urinary tract consists of the organs, tubes, and muscles that work together to make, move, store, and release urine. The upper urinary tract includes the kidneys, which filter wastes and extra fluid from the blood, and the ureters, which carry urine from the kidneys to the bladder. The lower urinary tract includes the bladder, a balloon-shaped muscle that stores urine, and the urethra, a tube that carries urine from the bladder to the outside of the body during urination. If the urinary system is healthy, the bladder can hold up to 16 ounces -- 2 cups -- of urine comfortably for 2 to 5 hours.
Muscles called sphincters squeeze shut the tubes from the bladder to help keep urine from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder, which leads into the urethra.
Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to go. The sensation to urinate becomes stronger as the bladder continues to fill. As it reaches its limit, nerves from the bladder send a message to the brain that the bladder is full and the urge to empty your bladder intensifies.
When you urinate, the brain signals the bladder muscle to tighten, squeezing urine out of the bladder. At the same time, the brain signals the sphincter muscles to relax. As these muscles relax, urine exits the bladder through the urethra. When all the signals occur in the correct order, normal urination occurs.
What causes urinary retention?
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Urinary retention can be caused by an obstruction in the urinary tract or by nerve problems that interfere with signals between the brain and the bladder. If the nerves aren't working properly, the brain may not get the message that the bladder is full. Even if you know that your bladder is full, the bladder muscle that squeezes urine out may not get the signal that it is time to push, or the sphincter muscles may not get the signal that it is time to relax. A weak bladder muscle can also cause retention.
Nerve disease or spinal cord injury
Many events or conditions can damage nerves and nerve pathways. Some of the most common causes are
In addition, some children are born with nerve problems that can keep the bladder from releasing urine.
Prostate enlargement: benign prostatic hyperplasia
As a man ages, his prostate gland may enlarge. Doctors call the condition benign prostatic hyperplasia (BPH), or benign prostatic hypertrophy.
As the prostate enlarges, the layer of tissue surrounding it stops it from expanding, causing the gland to press against the urethra like a clamp on a garden hose. As a result, the bladder wall becomes thicker and irritable. The bladder begins to contract even when it contains small amounts of urine, causing more frequent urination. Eventually, the bladder weakens and loses the ability to empty itself, so urine remains in the bladder.
Infections cause swelling and irritation, or inflammation. A urinary tract infection (UTI) may cause retention if the urethra becomes inflamed and swells shut.
During surgery, anesthesia is often administered to block pain signals, and fluid is given intravenously to compensate for possible blood loss. The combination may result in a full bladder with impaired nerve function. Consequently, many patients have urinary retention after surgery.
Many medicines work by calming overactive nerve signals. Various classes of drugs that block various signals may be used to treat allergies, stomach cramps, muscle spasms, anxiety, or depression. Some medicines are used to treat urinary incontinence and overactive bladder. The drugs that may cause urinary retention include
A stone formed anywhere in the urinary tract may become lodged in the bladder. If the stone is large enough, it can block the opening to the urethra like a bathtub plug.
Cystocele and rectocele
A cystocele occurs when the wall between a woman's bladder and her vagina weakens and allows the bladder to droop into the vagina. The abnormal position of the bladder may cause urine to remain trapped. In a rectocele, the rectum droops into the back wall of the vagina. Cystocele and rectocele are often the results of a dropping of the pelvic support floor for the bladder. This sagging can pull the bladder out of position and cause urinary problems such as incontinence or urinary retention.
A hard stool in the rectum may push against the bladder and urethra, causing the urethra to be pinched shut, especially if a rectocele is present.
A stricture is a narrowing or closure of a tube. Men may have a narrowing of the urethra, usually caused by scarring after a trauma to the penis. Infection is a less common cause of scarring and closure in the urethra.
Medically Reviewed by a Doctor on 4/18/2014
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