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Urinary System Anatomy

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Updated November 04, 2009

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

The "urinary system" consists of two kidneys and two ureters, and a single bladder and urethra. The urinary system has several important tasks, including:

  • to filter waste products from your blood
  • to produces and transport those waste products -- known as urine -- from your body, all through connected organs and tubes
  • to maintain fluid balance
  • to control red blood cell production by secreting the hormone erythropoietin
  • to regulate normal blood pressure by secreting the enzyme renin.

1. What does each part of the urinary system do?

The kidneys are where the urinary system's work begins. Located in the back of your abdomen, they are two bean-shaped organs that in adults measure about 5 inches long and 2 inches wide, and weigh about 5 ounces each.

The kidneys remove excess water, salts, and metabolic wastes and toxins from the blood. This filtering process results in the production of urine.

You have two hollow, cylindrical ureters that extend down from each kidney into the bladder, carrying urine.

The bladder stores the urine until the bladder is full. Although it is hollow, it has a flexible muscular sac that pushes the urine down into the urethra.

The urethra is a duct that carries the urine from the urinary bladder to the outside when you urinate.

2. How do you learn to control when you urinate?

Children learn to recognize the signals that their bladder is full in the few years of life during toilet training. Sometimes they watch their parents urinate and imitate them, urinating only when they get to the toilet.

3. What happens when you lose control and urinate when you don't want to?

You develop urinary incontinence, a technical term for when you are unable to contain your urine. Depending on what is wrong in the urinary tract, surrounding structures, and elsewhere in the body, different strategies may prove effective in helping you contain your urine.

4. What should you do if you cannot urinate?

You should see your doctor immediately. Being unable to urinate, also known as urinary retention, often is an emergency situation.

Sometimes this occurs after surgery near the urinary tract. In that case, you should ask your doctor when you should be concerned.

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