The anus is a sphincter at the end of the rectum through which passes stool during defecation. The anal sphincter is a critical mechanism for control of fecal continence.
Review Date 5/6/2022
Updated by: Michael M. Phillips, MD, Emeritus Professor of Medicine, The George Washington University School of Medicine, Washington, DC. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.