The anal sphincter is a ring of muscle that controls the opening and closing of the anus.
The sphincter muscle helps regulate the passage of substances through various openings in the body.
The lower esophageal sphincter is a muscular ring that controls the flow of food between the esophagus and stomach.
The urinary sphincter is a muscle that helps control the flow of urine from the bladder.
The internal anal sphincter is a smooth muscle that is not under voluntary control.