Physiology, Defecation

Excerpt

Defecation is the term for the act of expelling feces from the digestive tract via the anus. This complex function requires coordination between the gastrointestinal, nervous, and musculoskeletal systems. The process begins with mass movement from the colon to the rectum, initiating the defecation reflex, which involves rectal contraction and internal and external anal sphincter relaxation. Defecation is involuntary from the colon to the internal anal sphincter, where smooth muscles push feces out. However, it is under conscious or subconscious control at the level of the external anal sphincter, which is lined by striated muscles (see Image. Defecation Reflex).

This article focuses on the physiologic process driving defecation.