Anorectal Anatomy and Physiology

The anorectal canal has the important function of regulating defecation and the role of controlling fecal continence. To fulfill its function, it is necessary to integrate muscular and sensory components. Continence in normal conditions is maintained by the acute angle that the contraction of the pubo-rectal muscle creates at the recto-anal junction, the rectal compliance, and the area of high pressure 2 cm from the anal verge. The resting pressure of the channel is attributed by 80 % to the tonic contraction of the internal anal sphincter, and the remaining 20 % is due to the action of the external anal sphincter and a small part of the hemorrhoidal cushions. During the filling of bulb, the distension of the rectum evokes the reflex inhibition of anal canal, with relaxation of the internal sphincter and contraction of the external sphincter. During defecation the external anal sphincter is voluntarily inhibited, the pubo-rectal muscle is relaxed with the aid of the abdominal muscles, and the fecal material is pushed out of the intestine.