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The anatomy and physiology of normal anorectum


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Talk delivered at MAMC Pediatric Update

Published in: Health & Medicine, Business

The anatomy and physiology of normal anorectum

  1. 1. Pediatric Surgery Update April 2o10” MAMC New Delhi
  2. 2. Scope 26
  3. 3. Ano-rectal anatomy <ul><li>Rectum </li></ul><ul><ul><li>Hind gut termination starting opposite the sacral promontory </li></ul></ul><ul><ul><li>With no haustrations and tenaea converging to form longitudinal muscle coat </li></ul></ul><ul><ul><li>The middle dilated part is the ampula with mucosal valves </li></ul></ul><ul><ul><li>Has a normal angle of 120 deg with the anal canal </li></ul></ul>25
  4. 4. Ano-rectal anatomy <ul><li>Anal canal </li></ul><ul><ul><li>Commences at the level where the rectum passes through the pelvic diaphragm and ends at the anal verge. </li></ul></ul><ul><ul><li>Dentate line </li></ul></ul><ul><ul><li>Anal valves </li></ul></ul>24
  5. 5. The anatomy of continence 23 The ability to retain-voluntarily or involuntarily-the intestinal contents until an evacuation is desired”. Holschneider
  6. 6. The anatomy of continence 22
  7. 7. Levator ani <ul><li>Conglomeration of 3 striated muscles </li></ul><ul><ul><li>Puborectalis </li></ul></ul><ul><ul><li>Pubococcygeous </li></ul></ul><ul><ul><li>Illiococcygeous </li></ul></ul><ul><li>Puborectalis is innermost and merges with the external anal sphincter. It causes the 120 deg angulation of anorectum due to the pull against the pubic bones </li></ul><ul><li>By its action it also shuts the lumen by apposing the post and the side walls of rectum </li></ul>21
  8. 8. <ul><li>Puborectalis </li></ul><ul><ul><li>Originates from myotomes S1-S4 </li></ul></ul><ul><li>Pubo coccygeous and illiococcygeous help to close the urogenital diaphragm by voluntary contraction, as well as elevate, straighten steady and suspend the rectum. </li></ul><ul><li>They are helped by the perineal body in the suspending action </li></ul>20 PR IC PC
  9. 9. The External Sphincter <ul><li>Three part striated muscle (slow twitch)forming a collar around the middle and the lower part of anal canal </li></ul>19
  10. 10. The External Sphincter <ul><li>Triple loop system </li></ul>18 Female
  11. 11. <ul><li>The superficial external sphincter </li></ul><ul><li>Deep part of ext sphincter </li></ul><ul><ul><li>Continuous with the puborectalis </li></ul></ul><ul><li>Subcutaneous part with the corrugate cutis ani </li></ul>17
  12. 12. <ul><li>Circular layer of rectum be-comes internal anal sphincter </li></ul><ul><li>Longitudinal layer of rectum becomes intersphincteric fascial plane </li></ul><ul><li>Muscle responsible for the recto-anal inhibitory response (RAIR) on manometery. </li></ul>Internal anal sphincter
  13. 13. Continence dynamics 15 <ul><li>Continence during sleep and rest is by the continuous tonic contraction of the Internal sphincter </li></ul><ul><li>Continence during raised intra abdominal pressure is by the levator ani and the external sphincter </li></ul>
  14. 14. Supportive structures for continence <ul><li>Perineal body </li></ul><ul><ul><li>4 muscles 2 paired 2 unpaired </li></ul></ul><ul><ul><li>Superficial transverse perinei, deep transverse perinei (paired) </li></ul></ul><ul><ul><li>Arching fibers of puborectalis around the rectum+fibers of bulbospongiosus (unpaired) </li></ul></ul><ul><li>Anorectal angle </li></ul><ul><li>Rectal ampula </li></ul><ul><li>Mucosal valves </li></ul>14
  15. 15. 13 Spinal control by Onuf Nucleus
  16. 16. <ul><li>Pudendal nerve supplies to </li></ul><ul><ul><li>All 3 muscles of levator ani </li></ul></ul><ul><li>nervierigentis </li></ul><ul><ul><li>Distal most nerve fibers relay on to the ganglia of aurbachs plexus </li></ul></ul><ul><ul><li>The parasympathetic nerves follow the path of major blood vessels to rectum </li></ul></ul><ul><ul><li>Sensory reflex of rectal distention </li></ul></ul><ul><li>Presacral sympathetic nerves </li></ul><ul><ul><li>Motor to involuntary internal sphincter </li></ul></ul><ul><ul><li>Inhibitors of bowel wall motion </li></ul></ul>12
  17. 17. Physiological coordination responsible for continence 11
  18. 18. 10
  19. 19. Fine control over defecation reflex <ul><li>Mucosa over pecten contains </li></ul><ul><ul><li>Nerve endings - pain </li></ul></ul><ul><ul><li>Meisseners corpuscules – touch </li></ul></ul><ul><ul><li>Krause end organs – pressure </li></ul></ul><ul><ul><li>Pacini corpuscules - friction </li></ul></ul><ul><li>The relaxation of the internal sphincter allows the contents to come in contact with the above sensory receptors. </li></ul><ul><li>They are able to discriminate air v/s solid fecal matter </li></ul><ul><li>The relaxation of external sphincter will occur if air is leading the flow – if one wants. </li></ul>9
  20. 20. 8
  21. 21. 7
  22. 22. Defecation reflex 6 Initiation by voluntary abdominal contraction, gastrocolic reflex, colonic reflex, direct rectal mucosal stimulation, rectal distention Filling and distension of lower rectum Increase rectal pressure Stimulation of receptors in the pelvic floor – desire to defecate- relaxation of the internal sphincter If not voluntary inhibited The external sphincter also relaxes No social opportunity, contraction of external anal sphincter and puborectalis- Rectal adaptation occurs Defecation
  23. 23. 5
  24. 24. Aberrations in ARM- structural 4
  25. 25. Anatomy as seen during PSARP <ul><li>During posterior saggital approach we see two groups of muscle fibres </li></ul><ul><ul><li>One group running in vertical direction (on table PSARP position) </li></ul></ul><ul><ul><li>2 nd group more bulky running in transverse direction merging with levator within the depth of incision </li></ul></ul>3 The vertical group also know as the para saggital fibers are a part of the external sphincter and are presumably its superficial part
  26. 26. Anatomy as seen during PSARP <ul><li>The lower transverse fibers are the muscle complex fibers (as termed by Pena et al) is also the external sphincter part which converge with the levator ani in deeper planes at almost right angles. </li></ul><ul><li>This muscle complex is perpendicular to para saggital fibers. </li></ul><ul><li>The crossing of the muscle complex creates the anterior and the posterior limit of the neo anus </li></ul><ul><li>The levator muscle lies deeper in the incision and higher the malformation </li></ul><ul><li>deeper is the levator </li></ul>
  27. 27. Abberations in ARM- neural 1
  28. 28. 0 Thank you