Assertion: urethra's sphincter | /r/CapableOf | keep the urethra
Facets:
Source sentences:
text: At the bladder-urethral junction, a thickening of the smooth muscle forms the internal urethral sphincter, an involuntary sphincter that keeps the urethra closed when the urine is not being passed.
text: At the bladder-urethral junction, a thickening of the smooth muscle forms the internal urethral sphincter, an sphincter that keeps the urethra closed when the urine is not being passed.