Internal Urethral Sphincter is formed by which structure?

Internal Urethral Sphincter is formed by which structure?

• A. Thickening of smooth muscle where bladder connects to urethra
• B. Skeletal muscle
• C. Cardiac muscle
• D. Nervous tissue

Answer: (A)

The internal urethral sphincter is formed by a thickening of smooth muscle at the bladder neck where the bladder transitions to the urethra. This smooth muscle form makes it an involuntary sphincter under autonomic control, helping maintain continence by keeping the urethra closed as the bladder fills and relaxing to allow urine flow during micturition. The external urethral sphincter, in contrast, is skeletal muscle and under voluntary control, which is why it’s not the internal sphincter. Cardiac muscle and nervous tissue do not form the urethral sphincters.

The internal urethral sphincter is formed by a thickening of smooth muscle at the bladder neck where the bladder transitions to the urethra. This smooth muscle form makes it an involuntary sphincter under autonomic control, helping maintain continence by keeping the urethra closed as the bladder fills and relaxing to allow urine flow during micturition. The external urethral sphincter, in contrast, is skeletal muscle and under voluntary control, which is why it’s not the internal sphincter. Cardiac muscle and nervous tissue do not form the urethral sphincters.