The Kidneys and Urinary System

The urinary system includes those organs of the body that produce and eliminate urine (a combination of water and waste products that passes out of the body as fluid).  By controlling urine flow, the system maintains proper water balance in the body.  Individual parts of the urinary system monitor the concentration of salts and other necessary nutrients. 

Functions of Organs

The organs most responsible for the control of the balance of chemicals and water in the blood are the two kidneys.  The kidneys are bean-shaped structures located in back of the abdomen.  Their chief functions are to filter wastes from the blood and to ensure reabsorption of essential chemicals back into the bloodstream.  The kidneys also play a major role in blood pressure regulation, and they influence the production of red blood cells.  In the kidneys, waste products combine with water and salts to form urine.  Urine passes from each kidney into the bladder through tubes called ureters.  The bladder stores the urine until elimination.  

A sphincter muscle surrounding the exit from the bladder prevents urine from escaping.  When the bladder is about half full, the body feels an urge to urinate.  At this time, the muscle can be relaxed voluntarily to release the urine and empty the bladder during the elimination process.  The urethra is a tube that transports urine from the bladder to the exterior of the body.  The female urethra is about an inch-and-a-half long and is enclosed within the body.  The male urethra passes through the penis and is approximately eight inches long.  For the male, the urethra serves the dual function of transporting urine and semen (the fluid from the male reproductive organs).  Semen is released during sexual intercourse, at which time urine is blocked from leaving the bladder. 

Disorders

Changes in urine and urinary habits that do not seem to have an obvious cause may be symptoms of disease.  Some symptoms that require medical attention are changes in frequency, timing, and control of urination; changes in the quantity and color of urine; and the presence of pain accompanying urination.  A doctor should be contacted if any of the following symptoms is noted: extreme pain while urinating, blood in the urine, a noticeable increase or decrease in frequency of urination (a symptom of kidney failure), marked changes in the color of the urine, or cloudiness in the urine accompanied by pain or fever.  Changes in urine or urinary habits may be caused by a variety of disorders involving the kidneys, urinary tract, bladder, and prostate (a gland that surrounds the male urethra).  Increased frequency of urination may be caused by inflammation of the kidneys, bladder, or urethra; diabetes mellitus (a disorder of carbohydrate metabolism); or an enlarged prostate gland.  A change in timing of urination, usually in the form of very frequent nighttime awakenings accompanied by the urge to urinate (called nocturia), is often coupled with painful urination, a weak stream, or difficulty in starting urination.  These may be symptoms of an enlarged prostate gland or an inflammatory or infectious disease within the urinary tract, as well as tumors or other disorders that result in increased pressure on the bladder.  Difficulty in controlling, starting, and maintaining the flow of urine may also be symptoms of an inflammation of the prostate gland.  Inability to hold back urine is a common problem of elderly people, as their control of the sphincter muscle of the bladder weakens.  Also affected by this problem are women who are in the late stages of pregnancy, when the enlarged uterus continuously presses on the bladder.  Changes in the quantity of urine normally produced can also be an indication of disease.  Producing an excessive amount of urine (called polyuria) may be a symptom of kidney disease, diabetes, or glandular disorders.  Decreased production of urine may indicate the presence of dehydration, internal hemorrhaging, or acute renal failure.  Slight changes in the color and clarity of the urine from day to day are normal, but strikingly obvious color changes and extreme cloudiness may signal infection, tumors, kidney stones, prostate problems, or other abnormalities in the urinary tract.  Pain while urinating, most commonly in the form of a burning sensation felt along the urethra, may be a sign of a lower urinary tract infection.  Excruciating pain across the abdomen or the back may signal the presence of kidney stones.  Treatment of urinary problems usually involves treating an underlying cause, which can range from a mild infection to a very serious disease.  An accurate diagnosis by a physician is the first step to proper treatment of these disorders.