Anatomy of Lower Gastrointestinal Tract

1. Anatomy of Lower Gastrointestinal Tract Thanasil Huanmanop MD, M.ScAnatomy Chula

2. LGIT = duodenojejunal junction - anus :Jejunoileum, large intestine & anal canal

3. Embryology : Foregut, Midgut, Hindgut Vitelline duct

4. Small intestine - Jejunoileum :>duodenojejunal junction - ileocaecal junction ( 20 ft )> proximal 1/3 LUQ , middle 1/3 periumbilical , distal 1/3 pelvis

5. Ligament of Treitz:duodenojejunal flexure (L2) - Rt. crus of diaphragm Right crus of diaphragm Ligament of Treitz Celiac trunk jejunum duodenum Lower GI tract

6. Ileocaecal junction :Line ( Rt. ASIS - umbilicus ) X Rt. linear semilunaris , L5

7. Jejunoileum Intraperitoneal organ Anterior : greater omentum ( omental apron ) Posterior : mesentery properto post. abdominal wall • double-layered peritoneal fold • root 6-7 inches Root of mesentery Mesentery proper

8. Jejunum Ileum

9. Clinical consideration: • Resect mesentery of jejunoileum -> intestinal mobile • Resection of small bowel : short bowel syndrome (80%) • Cancer, Inflammation, hemorrhage, obstruction

10. MECKEL’S DIVERTICULUM • Remnant of vitelline duct • Organ of 2 = 2% , 2 ft from IC valve , 2 inches, 2 special types of mucosa (gastric & pancreatic) • Bleeding / diverticulitis

11. Large intestine : 5 ft ; ileocaecal junction - anus Transverse colon Splenic flexure Hepatic flexure Descending colon Ascending colon Ileocecal junction Caecum Sigmoid colon Vermiform appendix Rectum Anal canal

12. General features of large intestine :

13. Caecum : 7.5 x 6 cm., blind intestinal pouch, Rt. iliac fossa (L5)Ileocaecal orifice : ileocaecal valve (superior & inferior lips), frenulum Appendicular orifice Mesenteric support :- Superior ileocaecal (vascular) fold & fossa- Inferior ileocaecal fold & fossa- Rectocaecal fossa Clinical consideration : • Fecal reflux at IC valve • Intussusception

14. Vermiform appendix 10 cm., blind intestinal diverticulumsearch by following taenia coliIntraperitoneal organ –mesoappendix RLQ at McBurney’s point :Lat. 1/3 & med. 2/3 of line ( Rt. ASIS - umbilicus )malrotation or nonrotation, situs inversusPosition : retrocaecal , pelvic

15. Clinical consideration : Acute appendicitis • common abdominal emergency • lymphoid hyperplasia & fecolith • appendiceal mass/abscess • appendectomy • McBurney’s incision…?

16. Ascending colon :20 cm., Rt. lumbar regionRt. colic (hepatic) flexureSecondarily retroperitoneal organ Volvulus(L.volvo=to roll)

17. Transverse colon : 45 cm., umbilical region intraperitoneal organ hepatic flexure -Lt. colic (splenic) flexure(phrenococolic or sustenaculum lienis) Transverse mesocolonGreater omentum & gastrocolic lig.

18. Descending colon : 25 cm., Lt. hypochondriac, lumbar & iliac regionssplenic flexure to Lt. pelvic brim Secondarily retroperitoneal organ

19. Sigmoid colon :40 cm., S-shape, suprapubic region, intraperitoneal organ Rectosigmoid junction (15 cm. from anus, S3) Sigmoid mesocolon (reverse V-shape) & intersigmoid fossa

20. Clinical consideration : • Variation • Sigmoid volvulus

21. Rectum :15 cm., extraperitoneal organ, rectosigmoid junction to anorectal ring(pelvic diaphragm) S3 3 parts of rectum andPeritoneal reflections : anterior, lateral & posterior

22. Rectum : Pararectal fossa Mesorectum Rectouterine pouch (pouch of Douglas or Cul-de-sac) Rectovesical pouch Rectovesical septum or Denonvillier’s fascia Rectovaginal septum

23. Rectum :No mesentery, haustra coli, appendices epiploicae, taenia coli spread out and form longitudinal rectal muscleRectal ampulla : fecal storage before defecationTransverse rectal folds (shelves)(Houston’s valves) Taenia coli spread to form Longitudinal rectal muscle Right middle rectal valve* Left upper (Supr) rectal valve Rectal ampulla Left lower (Infr) rectal valve Levator ani muscle (pelvic diaphragm) * Anterior peritoneal reflection

24. Clinical consideration : Colorectal carcinoma • Most at rectum • large bowel obstruction • Colectomy • Colostomy • Barium enema • Colonoscopy, sigmoidoscopy, proctoscopy

25. Clinical consideration : • Digital rectal examination (DRE) or PR(per rectum) -> prostate gland, rectal mass • Megacolon (Hirschprung’s disease)- congenital, absent of parasympathetic ganglion cell in myenteric plexus of intestinal wall • Polyp / Diverticulum

26. Anal canal :Terminal part of LGIT, 3-4 cm. Anorectal ring (pelvic diaphragm) - anus (anal opening, anal verge) Ant. : perineal body, urogenital diaphragm, bulb of penis or vaginaPost. : anococcygeal raphe’Upper : pelvic diaphragm Anorectal ring Anus, anal verge Levator ani muscle (pelvic diaphragm)

27. Wall of anal canal :Internal sphincter ani (involuntary) External sphincter ani (voluntary) Pelvic diaphragm (Levator ani muscle) (rectal sling) Conjoined longitudinal muscle ( from levator ani muscle & outer longitudinal muscle of rectum) Deep external sphincter ani muscle Superficial external sphincter ani muscle Internal sphincter Ani (from inner circular muscle of rectum) Corrugator cutis ani muscle Subcutaneous external sphincter ani muscle * Anorectal ring : check sphincter tone by DRE, protect fecal incontinence

28. Mucosa of anal canal : Anal columns (of Morgagni) Rectal venous plexus Dentate (pectinate) line Anal valves Anal crypts (sinuses) Opening of anal glands Transitional (intermediate) Zone or pecten Hilton white line Cutaneous zone

30. Hemorrhoids or piles :