After our bodies have taken what they need from our foods, waste products are left behind in the blood (and the bowel). The urinary system plays a critical role in eliminating wastes and keeping the chemicals and water in our bodies balanced. Most adults void about a quart and a half of urine each day, with the amount depending on many factors, including the amounts of fluid a person consumes and how much fluid is lost through sweat and breathing.

The urinary system removes a waste called “urea” from the blood. This is produced when foods containing protein are broken down. Urea is carried in the bloodstream to the kidneys, which are bean-shaped organs located near the middle of the back and just below the rib cage. They remove urea from the blood through tiny filtering units called “nephrons.” Urea, water, certain minerals and other pass from the nephrons into tiny tubules which drain into the kidney´s central collecting system.

From the kidneys, urine travels down two thin tubes called “ureters” to the bladder. Smooth muscles in the ureter walls constantly tighten and relax to create peristaltic waves which force urine downward from the kidneys.  As a result, small amounts of urine are emptied into the bladder from the ureters every 10 or 15 seconds.  A blockage of the ureter from a stone will cause pain by interfering with the flow of urine and over stretching the muscles of the ureter above the stone. Infection and damage to the kidney can also occur as a result of this obstruction.

The bladder is a hollow muscular organ that is like a balloon. It sits in the pelvis and is held in place by ligaments attached to other organs and to the pelvic bones. The bladder stores urine until a person is ready to go to the bathroom. In healthy people, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for several hours.

Circular muscles called “sphincters” prevent the bladder from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the tube called the “urethra”, This is the tube that carries urine outside the body.

Nerves in the bladder make the person aware of the need to urinate. As the bladder first fills with urine, one may feel the need to urinate. This can be suppressed for a time, but the sensation to urinate becomes stronger as the bladder continues to fill. When it reaches capacity, nerves from the bladder send a message to the brain that the bladder is full, and the urge to empty the bladder very much intensifies.

When one urinates, the brain signals the bladder muscles to tighten, squeezing urine out of the bladder. while at the same time, signaling the sphincter muscles to relax. As these muscles relax, urine leaves the bladder through the urethra.



The organs, tubes, and muscles that work together to create, store, and carry urine make up the urinary tract. The tract includes two kidneys, two ureters, the bladder, two sphincter muscles, and the urethra.


“Urinalysis” is a test that studies the content of urine for abnormal substances such as protein or signs of infection. The patient urinates into a special container and leaves the sample to be studied.

“Urodynamic” tests evaluate the storage of urine in the bladder and the flow of urine from the bladder through the urethra. A doctor may want to do a urodynamic test if his patient has symptoms that suggest problems with the muscles or nerves of the lower urinary system and pelvis (ureters, bladder, urethra, and sphincter muscles).

Urodynamic tests measure the contraction of the bladder muscle as the organ fills and empties. The test is done by inserting a small tube called a catheter through the urethra into the bladder to fill it with either water or a gas. Then another tube is inserted into the rectum to measure the pressure put on the bladder by the patient’s straining or coughing.

Other bladder tests use x-ray dye instead of water so that x-rays can be taken when the bladder fills and empties. These films may detect any abnormalities in the shape and function of the bladder.


“Benign prostatic hyperplasia” (BPH) is a condition in men that affects the prostate gland. The prostate is located at the bottom of the bladder and surrounds the urethra. BPH is an enlargement of the prostate gland that can interfere with urinary function in older men. It causes blockage that can make it difficult to urinate. Sufferers frequently have other bladder symptoms that include an increase in urinary frequency both during the day and at night. Although most men over age 60 have some BPH, not all have problems with blockage. There are many different treatment options for BPH that are highlighted in other sections of this website.

“Kidney stones” is the term commonly used to refer to deposits called “calculi” in the urinary system. Stones form in the kidneys and vary considerably in size. They may be found anywhere along the urinary tract. Some stones cause great pain while others cause very little. The aim of treatment is to remove the stones and prevent infection or recurrence. Both nonsurgical and surgical treatments are used.

Prostatitis is inflammation of the prostate gland that results in urinary frequency and urgency, burning or painful urination (dysuria), and pain in the lower back and genital area. In some cases, prostatitis is caused by bacterial infection and can be treated with antibiotics. But the more common forms of prostatitis do not appear to result from infection, and, therefore, antibiotics are often ineffective as treatment.

Urinary tract infections (called “UTIs”) are caused by bacteria in the urinary tract. Women get UTIs more often than men and generally respond well to treatment with antibiotics. Drinking lots of fluids also helps by flushing out the bacteria. The name of the UTI depends on its location in the urinary tract, with infection in the bladder being called “cystitis” and Infection in the kidney being called “pyelonephritis”. The latter can cause serious damage to the kidneys if it is not adequately treated.

Urinary incontinence, or loss of bladder control, is the involuntary passage of urine. There are many causes of incontinence and treatments range from simple exercises to surgery. Women are affected by urinary incontinence more often than men.

Urinary retention, or difficulty in emptying the bladder, is a common urological problem with many causes. Under normal circumstances, urination can be initiated voluntarily and the bladder will empty completely. In urinary retention, urine is abnormally held in he bladder. When this happens suddenly, (“acute urinary retention”), it can cause pain and considerable distress. Causes can include an obstruction in the urinary system, stress, or neurologic problems. Chronic urinary retention refers to the regular presence of urine in the bladder after incomplete emptying. Common causes of are bladder muscle failure, nerve damage, or obstructions in the urinary tract.