Normally, the bladder begins to fill with urine from the kidneys. The bladder stretches to allow more and more urine.
You should feel the first urge to urinate when there is around 200 mL (just under 1 cup) of urine stored in your bladder. A healthy nervous system will respond to this stretching sensation by letting you know that you have to urinate. At the same time, the bladder should keep filling.
The average person can hold around 350 to 550 mL (more than 2 cups) of urine in the bladder. Two muscles help control the flow of urine:
- The sphincter (the circular muscles around the opening of the bladder) must be able to squeeze to prevent urine from leaking.
- The bladder wall muscle (detrusor) must stay relaxed so the bladder can expand.
When it is time to empty the bladder, the bladder wall (detrusor) muscle contracts or squeezes to force urine out of the bladder. Before this muscle squeezes, your body must be able to relax the sphincter to allow the urine to pass out of your body.
To control urination, you must have:
- A working urinary system
- A working nervous system
- The ability to feel and respond to the urge to urinate
Incontinence is most common among the elderly. Women are more likely than men to have urinary incontinence.
Infants and children are not incontinent before they have been toilet trained. Children up to age 6 may still have accidents sometimes. Young (and sometimes teenage) girls may leak a little bit of urine when they laugh.
It is normal for children to wet the bed until age 5 or 6.
Bladder function - neurological control