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

Your body takes nutrients from food and uses them to maintain all bodily functions including energy and self-repair. After your body has taken what it needs from the food, waste products are left behind in the blood and in the bowel. The urinary system works with the lungs, skin, and intestines—all of which also excrete wastes—to keep the chemicals and water in your body balanced. Adults eliminate about a quart and a half of urine each day. The amount depends on many factors, especially the amounts of fluid and food a person consumes and how much fluid is lost through sweat and breathing. Certain types of medications can also affect the amount of urine eliminated.

The urinary system removes a type of waste called urea from your blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

The kidneys are bean-shaped organs about the size of your fists. They are near the middle of the back, just below the rib cage. The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

From the kidneys, urine travels down two thin tubes called ureters to the bladder. The ureters are about 8 to 10 inches long. Muscles in the ureter walls constantly tighten and relax to force urine downward away from the kidneys. If urine is allowed to stand still, or back up, a kidney infection can develop. Small amounts of urine are emptied into the bladder from the ureters about every 10 to 15 seconds.

The bladder is a hollow muscular organ shaped like a balloon. It sits in your pelvis and is held in place by ligaments attached to other organs and the pelvic bones. The bladder stores urine until you are ready to go to the bathroom to empty it. It swells into a round shape when it is full and gets smaller when empty. If the urinary system is healthy, the bladder can hold up to 16 ounces (2 cups) of urine comfortably for 2 to 5 hours.

Circular muscles called sphincters help keep urine from leaking. The sphincter muscles close tightly like a rubber band around the opening of the bladder into the urethra, the tube that allows urine to pass outside the body.

Nerves in the bladder tell you when it is time to urinate (empty your bladder). As the bladder first fills with urine, you may notice a feeling that you need to urinate. The sensation to urinate becomes stronger as the bladder continues to fill and reaches its limit. At that point, nerves from the bladder send a message to the brain that the bladder is full, and your urge to empty your bladder intensifies.

When you urinate, the brain signals the bladder muscles 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.

Medicines can affect bladder control in different ways. Some medicines help prevent incontinence by blocking abnormal nerve signals that make the bladder contract at the wrong time, while others slow the production of urine. Still others relax the bladder or shrink the prostate. Before prescribing a medicine to treat incontinence, your doctor may consider changing a prescription you already take. For example, diuretics are often prescribed to treat high blood pressure because they reduce fluid in the body by increasing urine production. Some men may find that switching from a diuretic to another kind of blood pressure medicine takes care of their incontinence.

If changing medicines is not an option, your doctor may choose from the following types of drugs for incontinence:

Alpha-blockers: Terazosin (Hytrin), doxazosin (Cardura), tamsulosin (Flomax), and alfzosin (Uroxatral) are used to treat problems caused by prostate enlargement and bladder outlet obstruction. They act by relaxing the smooth muscle of the prostate and bladder neck, allowing normal urine flow and preventing abnormal bladder contractions that can lead to urge incontinence.

5-alpha reductase inhibitors: Finasteride (Proscar) and dutasteride (Avodart) work by inhibiting the production of the male hormone DHT, which is thought to be responsible for prostate enlargement. These 5-alpha reductase inhibitors relieve voiding problems by shrinking an enlarged prostate.

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) sponsored the Medical Therapy of Prostate Symptoms (MTOPS) trial, a multicenter study that found that doxazosin and finasteride taken together reduced the risk of BPH progression by 67 percent compared with placebo. The risk of progression was reduced by 39 percent with doxazosin alone and by 34 percent with finasteride alone.

Imipramine: Marketed as Tofranil, this drug belongs to a class of drugs called tricyclic antidepressants. It relaxes muscles and blocks nerve signals that might cause bladder spasms. Imipramine is also used to treat bedwetting in children.

Antispasmodics: Propantheline (Pro-Banthine), tolterodine (Detrol LA), and oxybutynin (Ditropan XL) belong to a class of drugs that work by relaxing the bladder muscle and relieving spasms. Their most common side effect is dry mouth, although larger doses may cause blurred vision,