Internal urinary sphincter

Definition

The internal urinary sphincter is a ring of smooth muscle located at the junction between the bladder and urethra that involuntarily controls the flow of urine. It automatically contracts to retain urine in the bladder and relaxes when the bladder contracts during urination.

Related terms

Urethra: The tube that transports urine from the bladder to be expelled from the body.

Detrusor Muscle: A layer of smooth muscle found in the bladder wall that contracts to expel urine.

Micturition: A process also known as urination, involving both voluntary and involuntary actions to release urine from the urinary bladder