Applied Anatomy of the Anal Canal

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Anatomy of the anal canal is very complex. It's understanding is very important on account of many common ailments in this area. The sphincters, spaces are important. Every medical student should be well versed in the anatomy of anal canal.

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Applied Anatomy of the Anal Canal

  1. 1. APPLIED ANATOMY OF THE ANAL CANAL
  2. 2. Definition  Surgical :   Anatomical :   The anal canal is the terminal portion of the intestinal tract it begins at the anorectal junction (the point passing through the levator ani muscles), is about 4 cm long, and terminates at the anal verge. that extends from the dentate line to the anal verge. Anteriorly   Male : bulb of urethra Female : perineal body and vagina
  3. 3.  Posteriorly :   Laterally   Coccyx and puborectalis muscle Ischio rectal fossa containing inferior hemorrhoidal vessels and pudendal nerve Surrounded below by external and internal sphincter muscles
  4. 4. The Rectum and anus
  5. 5. Anorectal ring Anoderm and Hilton’s line
  6. 6. Dentate line (pectinate line)
  7. 7. Dentate line (pectinate line)     Transition between the visceral area above and the somatic area below 2cm above & below this line forms “surgical anal canal” Anal columns Anal crypts
  8. 8. The Dentate line differntiate Fusion of proctodeum and post allontoic gut  Between cubical epithelium from squamous epithelium  Autonomic Nerves from the spinal nerves  Portal venous system to Systemic venous system 
  9. 9. Anal glands  80% are submucosal in extent, 8% extend to the internal sphincter, 8% to the longitudinal muscle, 2% to intersphincteric space, and  1% penetrate the external sphincter.   
  10. 10. Muscles of Ano-rectum
  11. 11. Ano-Rectal Muscles
  12. 12. ISHIORECTAL FOSSA --- The ischiorectal fossa is a pyramid shaped space . The apex is formed at the origin of the levator ani from the obturator fascia and the inferior boundary is the skin of the perineum . The anterior boundary is formed by the superficial & deep transversus pernei muscles and the posterior boundary of the perinei membrane. The posterior boundary is made up of the sacrotuberous ligament and the lower boarder of the Gluteus maximus muscles . The medial wall is composed of the levator anii muscles and the external sphincter muscles including the fascia that covers them . The lateral wall is nearly vertical , is formed by the obturator internus muscles, where it lies on the ischium & by the obturator fascia., in the obturator fascia ,on the lateral wall is alcocks canal which contains the internal pudendal vessels and pudendal nerve.
  13. 13. The contents of the ischiorectal fossa include a pad of fat , the inferior rectal nerve coursing from the back of the ischiorectal fossa forward and medially to the external sphincter ,interior rectal vessels ,portions of scrotal nerves & vessels in men and labial in women, the transverse perineal vessels and the pernial branch of the fourth sacral nerve running to the external sphincter form the posterior angle of the fossa .Anteriorly ischiorectal space has an important extention forward , above the urogenital diaphragm which may become filled with pus in cases of ischirectal abscesses.
  14. 14. Internal anal sphincter  Internal sphincter ( smooth muscle )  Downward and thickened extension of circular muscle fibres of rectum
  15. 15. Details of Internal sphincter The length :2.5 cms. Thickness Color Fibers Action Control :2-5 mm White Transversely placed Spasm or contracture Involuntary.
  16. 16. Details of the Internal Sphincter:  Color : Pink  Control : Involuntary  Divisions : Deep, superficial and subcutaneous.
  17. 17. External sphincter
  18. 18. External sphincter  Triple-loop system of Shafik.  The top loop arises and inserts on the pubis and is made up of the deep external sphincter and puborectalis.  The middle loop attaches to the coccyx (superficial external sphincter).  The lower loop inserts in the anterior perianal skin (subcutaneous external sphincter).
  19. 19. Pelvic floor
  20. 20. Arterial supply
  21. 21. Venous drainage
  22. 22. Nerve supply    Internal sphincter  sympathetic (L-5) &  parasympathetic nerves (S-2, S-3, and S4) External sphincter  inferior rectal branch of the pudendal nerve (S-2 ,S-3)  the perineal branch of S-4 Levator ani  sacral roots on its pelvic surface (S-2, S-3, and S-4)  perineal branch of the pudendal nerve
  23. 23. Lymphatic channels of anorectal region
  24. 24. Lymphatic drainage Upper anal canal Via channels around rectum into pre aortic nodes Lower anal canal Below dentate line Inguinal nodes
  25. 25. Lymph Nodes In and around Anal canal 
  26. 26. “Everything has been said before , but since not all listen , we have to keep going back and begin all over again.” A French author

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