Anatomy

The anal canal (anus) is 4 cm long and is continuous with the rectum above the pelvic floor. The mucous membrane of the upper half of the anal canal is lined by columnar epithelium and supplied by autonomic nerves, being sensitive only to stretch. The lower half is lined by stratified squamous epithelium and has a somatic nerve supply, being sensitive to pain, touch, etc. There is a transition zone with a sharp demarcation between the two types of mucosa, termed the dentate line. The circular muscle layer is thickened around the upper anal canal to form the internal (involuntary) sphincter. A sheath of striated muscle encloses this - the external (voluntary) sphincter. The longitudinal muscle coat descends between the internal and external sphincters. The ischiorectal fossa is a fat-filled space on either side of the anal canal between it and the bony pelvis (Figure 7.1).

Figure 7.1. The anatomy of the anal canal. Reproduced from Williams GR, Talbot IC. Anal carcinoma: a histological review. Histopathology 1994;25:507-516

Figure 7.2. Anus: regional lymph nodes. Perirectal (1), internal iliac (2) and inguinal (3). Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

Figure 7.2. Anus: regional lymph nodes. Perirectal (1), internal iliac (2) and inguinal (3). Reproduced from Hermanek P, Hutter RVP, Sobin LH, Wagner G, Wittekind Ch (eds.). TNM Atlas: illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

Was this article helpful?

0 0

Post a comment