Year 2009 Vol. 17 No 2

HYPOTHESIS

LEVIN M.D., TROYAN V.V.

ANATOMY AND PHYSIOLOGY OF ANORECTAL ZONE. HYPOTHESIS OF CONTINENCE AND DEFECATION

Based on our own investigations and literature analysis specification of our hypothesis of continence and defecation published earlier is presented here. The process of continence starts with inhibited passage of feces collected above the colonosigmoid and rectosigmoid sphincters and the anal canal. Feces density increases due to water absorption and its volume decreases.
Anterior displacement of the recto-anal connection contributes to feces continence. We suppose that multiple bundles of smooth muscle fibers in the internal anal sphincter (IAS) are present at different stages of the restoration of the contraction potential. Only mature bundles, i.e. bundles with large enough potential to contract, respond to electrical stimulus. Each next wave of electrical stimulation affects different bundles of fibers. This continuous process ensures high tonus of IAS 24 hours a day.
Interchanging continence reaction and reaction of adaptation promote prolonged fecal retention and vice versa. During contraction of one group of muscles, the other muscle group restores its contraction potential.
The reflex of defecation results in relaxation of the IAS, PRM, EAS and contraction of the musculus levator ani, which opens the anal canal up to the width of the rectum. Then, peristaltic wave of the rectum ensures propulsion of fecal masses.

Keywords: Rectum physiology, anal canal, continence, defecation, puborectal muscle, musculus levator ani, anorectal reflex
p. 105 - 118 of the original issue
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