title: A new concept of the anatomy of the anal sphincter mechanism and the physiology of defecation. IX. Single loop continence: a new theory of the mechanism of anal continence.
abstract: The role of the external and internal anal sphincters in the mechanism of anal continence is presented. The external sphincter induces continence by 1) preventing internal sphincter relaxation, what I have called the "voluntary inhibition action," and 2) mechanical compression of the rectal neck and anal canal proper. The mechanism of both actions is described. The internal sphincter plays a significant role not only in involuntary, but also in voluntary, continence. The importance of this role in the correction of anal incontinence is clarified. "Stress defecation," a condition which follows internal sphincter damage, is discussed. A "single loop continence" theory is presented, based on the fact that each of the three loops of the external sphincter has its own innervation, attachment, and direction of muscle bundles; each loop thus acts as a separate sphincter. The clinical application of this theory is presented.
mesh_terms: D001003:Anal Canal / Q000033:anatomy & histology* / Q000502:physiology / Q000601:surgery; D003672:Defecation; D005242:Fecal Incontinence / Q000601:surgery; D006801:Humans; D009119:Muscle Contraction; D012018:Reflex / Q000502:physiology