Medically Reviewed on April 24, 2013 by George Krucik, MD, MBA
Written and medically reviewed by the Healthline Editorial Team
Co-developed by:

In Depth: Bladder

The bladder, like the stomach, is an expandable sac that contracts with inner folds when it is empty. The inner lining of the bladder tucks into the folds and expand out to accommodate liquid.

When empty, the bladder’s muscle wall becomes thicker, and the entire bladder becomes firm. As the bladder fills from two ureters—tubes to expel urine from the kidneys to the bladder—the muscle wall thins, and the bladder moves upward toward the abdominal cavity.

This stretching can increase the size of the bladder from about 2 inches to more than 5 inches long, depending on the amount of liquid. The typical human bladder reaches its capacity between 16 to 24 ounces of urine, but the urge to urinate comes when the bladder is about one-quarter full.

An internal sphincter — a type of muscular valve — helps prevent urine from leaking out. The triangle-shaped base of the bladder, known as the trigone, helps prevent stretching of the urethra or backflow into the ureters.

When signaled, the bladder releases urine through the urethra, the tube that carries urine out of the body. In men, the urethra ends at the tip of the penis. In women, this tube ends between the clitoris and the vagina.

Healthy bladders hold urine until people have time to relieve themselves, but problems can arise for varying reasons.

Bladder infections and infections of the urinary tract are more common in women as they are more prone to outside bacteria than men. Also, women who have recently given birth may experience urinary problems.

Although rare in men, bladder infections do occur more often in older men. As they are uncommon, an infection could be a sign of something blocking the urinary tract or an even more serious problem such as cancer or kidney stones.

Men can also experience urinary problems due to complications with their prostate, a walnut-sized gland that surrounds the urethra.

Bladder control issues are common in women over the age of 50. Some of those conditions include:

  • Overactive bladder
  • Urinary incontinence
  • Stress incontinence
  • Neurogenic bladder
  • Flaccid bladder
  • Spastic bladder
  • Bladder stones
  • Bladder extrophy
  • Urinary retention
  • Cystitis

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