Mechanisms of continence

There are number of mechanisms which maintain continence:

• sigmo-rectal 'sphincter':
  • rectal contraction is a reflex response to filling
  • contraction is inhibited cortically
  • a temporary holdup of faeces at the acute angle of the pelvic loop of the sigmoid colon may aid continence
    
    
• ano-rectal angle:
  • the pubo-rectalis sling maintains the acute angle between the rectum and the anus, preventing passage of the stool into the anal canal
    
    
• anal sphincters:
  • external sphincter - striated muscle, voluntary
  • internal sphincter - smooth muscle
  • vascular cushions complete the seal
    
    
• ano-rectal sensation:
  • the ability to distinguish flatus and stool is especially important in the presence of diarrhoea

Reference:

1. Hayden DM, Weiss EG. Faecal incontinence: aetiology, evaluation, and treatment. Clin Colon Rectal Surg. 2011 Mar;24(1):64-70.
2. Rao SS. Pathophysiology of adult facal incontinence. Gastroenterology. 2004 Jan;126(1 suppl 1):S14-22.