What keeps urine from leaking?

The urinary sphincter muscles keep urine from leaking.

The internal urethral sphincter is a smooth muscle that is controlled by the autonomic nervous system. It is located at the bladder neck and helps to control the flow of urine from the bladder to the urethra. The external urethral sphincter is a skeletal muscle that is controlled by the somatic nervous system. It is located around the urethra and helps to prevent urine from leaking when the bladder is full.

When the bladder is full, the internal urethral sphincter relaxes and the external urethral sphincter contracts. This prevents urine from leaking out of the urethra.

When a person needs to urinate, the external urethral sphincter relaxes and the internal urethral sphincter contracts. This allows urine to flow out of the bladder through the urethra and exit the body.