Function: The anal canal serves to transmit and lubricate stool as it passes externally from the rectum, and the anorectal junction maintains continence, until by relaxation, the anorectal angle straightens, allowing defecation. The upper part of the canal is sensitive to stretch, but the lower part is sensitive to pain, touch and temperature, as well as stretch. The contral of the int. sph. m. is involuntary, and the contral of the ext. sph. is voluntary.