Anatomy and Physiology :
The gastrointestinal tract terminates in a short segment, the anal canal. Its external margin is poorly demarcated, but generally the skin of the anal canal can be distinguished from the surrounding perianal skin by its moist, hairless appearance. The anal canal is normally held in a closed position by action of the voluntary external muscular sphincter and the involuntary internal sphincter, the latter an extension of the muscular coat of the rectal wall.
The direction of the anal canal on a line roughly between anus and umbilicus should be carefully noted. Unlike the rectum above it, the canal is liberally supplied by somatic sensory nerves, so that a poorly directed finger or instrument will produce
The anal canal is demarcated from the rectum superiorly by a serrated line marking the change from skin to mucous membrane. This anorectal junction (often called the pectinate or dentate line) also denotes the boundary between somatic and visceral nerve supplies. It is readily visible on proctoscopic examination but is not palpable.
Subscribe to our Free Newsletters!