Circular muscle that helps keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

a ring of muscle that contracts to close an opening

A circular muscle that opens or closes like a drawstring. In the normal state, sphincter muscle contracts and is closed. When the muscle relaxes, it opens.

Any circular muscle in the body. A sphincter muscle helps keep urine from leaking around the opening of the bladder by closing tightly like a rubber band.

A circular band of muscle fibers that opens or closes a natural opening in the body; helps control bowel movements.

a circular muscle that opens and closes at an entrance to an organ. Examples include the lower esophageal sphincter and the anal sphincter.