Anal and Perianal Disorders

Abstract

<h2>Abstract</h2> <b>Lining of anal canal (Figure 1)</b> —the upper anal canal is lined with columnar epithelium; it has an autonomic nerve supply and is insensitive, except to distension. The lower anal canal is lined with stratified squamous epithelium similar to the adjacent skin, but without skin appendages; it has a somatic nerve supply and is exquisitely sensitive. The anal transition zone lies between these two areas, approximately at the level of the dentate line. The anal submucosa comprises largely blood vessels, some smooth muscle and connective tissue. Normal thickenings of the submucosa are termed 'anal cushions' and probably have a role in fine control of continence. About four to eight mucin-secreting glands open into the anal canal just above the dentate line.