Bedwetting in Children: Understanding the Urinary System

Around the age of three, most children begin to stay dry during the night. Occasionally, my three-year-old daughter will still wet the bed even though she has been potty trained since she was two. Usually, it's because she had too much to drink too close to bedtime or she was too tired to wake up and go to the bathroom. But more than this occasional type of accident can be concerning and frustrating for many parents.

"Our son had been potty trained for almost six months when he started wetting the bed all of a sudden," says Stephanie Fiedler, a Phoenix mother of three. "He'll be dry for a few weeks now and then wet the bed for a week straight. It's very random and can be frustrating since he was doing so well for months."

To understand why your child wets the bed, is taking longer to reach bladder control than his friends and how you can best help the situation, it is important to understand how the urinary system works in children, when you should consider it a problem and what you should do.

How does the urinary system work?

Urination is actually a complex process involving the bladder and the nervous system. The bladder is a balloon-like muscle that stores urine and then releases it through the urethra, the canal that carries urine to the outside of the body.

Control of urination involves nerves, muscles and the brain, according to the National Kidney and Urologic Diseases Information Clearinghouse (NIDDK).

According to NIDDK, the bladder is made up of two types of muscles that work together to control urination. The detrusor is a muscular sac that stores urine and squeezes to empty, while the sphincter is a circular group of muscles at the bottom (or neck) of the bladder that stay contracted to hold in the urine and then relax when the detrusor contracts to let the urine into the urethra.

There is a third group of muscles, the pelvic floor muscles, below the bladder that contract to keep urine in (when we all need to hold it!)

A baby's bladder actually fills to a certain point, and then automatically contracts and empties. But as a child gets older and the nervous system develops, the brain gets messages from the bladder that it is filling. The brain then sends messages to the bladder to keep it from automatically emptying until the child decides to go, hopefully once the child has reached the potty.

If there are failures controlling the bladder, it is called incontinence. Reasons for incontinence can be simple or complex.