Relaxation of the external urethral sphincter causes which of the following?

• A. Urine retention
• B. No effect
• C. Urine to flow through urethra
• D. Increased urinary frequency

Answer: (C)

Relaxation of the external urethral sphincter opens the exit from the bladder. This sphincter is a voluntary gate made of skeletal muscle that keeps the urethra closed when contracted. During voiding, signals from the nervous system inhibit the somatic nerves that keep the sphincter tight and allow it to relax, while the bladder detrusor muscle contracts to push urine out. So, when this sphincter relaxes, urine can flow through the urethra. That’s why the best answer is urine to flow through the urethra. Urine retention would occur if it stayed tight, increased frequency isn’t a direct result of sphincter relaxation, and no effect isn’t accurate because relaxation directly enables urination.