Anal Physiology: The Physiology of Continence and Defecation

  • Vitaliy Poylin
  • Thomas E. CataldoEmail author


The physiology of the anus and its surrounding structures is the physiology of continence and controlled defecation. This is a physiology of balance and continuous feedback and complex reflexes. Continence requires balance between the pressure inside the rectum and the combined tone of the internal and external sphincters. This chapter provides an overview of the anatomy, specifically the innervation of the anal complex with regard to how it affects normal and pathologic defecation. The neuro-sensory-motor aspects of the sequences of events of defecation are reviewed. Conditions that result in disordered defecation, pelvic pain, and complications outside the GI system are discussed.


Physiology Anorectal innervation Defecation Continence Pelvic floor RAIR Anorectal pain Obstructed defecation 



Rectoanal inhibitory reflex


Sacral nerve stimulation


Fecal incontinence


Magnetic resonance

Supplementary material

Video 3.1

Normal defecography (Courtesy of Shauna Lorenzo-Rivero, MD, FACS, FASCRS) (WMV 1122 kb)

Video 3.2

Defeocography of a patient with a rectocele (Shauna Lorenzo-Rivero, MD, FACS, FASCRS) (WMV 723 kb)


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Authors and Affiliations

  1. 1.Dept of Surgery, Division of Colon and Rectal Surgery etcBeth Israel Deaconess Medical Center, Harvard Medical SchoolBostonUSA
  2. 2.Dept of Surgery, Division of Colon and Rectal Surgery etcBeth Israel Deaconess Medical Center, Harvard Medical SchoolBostonUSA

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