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

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

Embryology : Foregut, Midgut, Hindgut Vitelline duct

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

Ligament of Treitz : duodenojejunal flexure (L 2 ) - Rt. crus of diaphragm duodenum jejunum Ligament of Treitz Celiac trunk Right crus of diaphragm Lower GI tract

Ileocaecal junction : Line ( Rt. ASIS - umbilicus ) X Rt. linear semilunaris, L 5

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

Characteristicjejunumileum Length8 ft (proximal 2/5 )12 ft (distal 3/5 ) Diameter2 – 4 cm2 – 3 cm WallThick and heavyThin and light ColorDeeper redPaler pink VascularityGreaterLess Vasa rectaLongShort Arterial arcadeA few large loopMany short loops Fat in mesenteryLessMore Plicae circulares ( circular folds ) Large,tall & closely packed Low & sparse VilliLarge & manySmall & discrete Peyer ’ s patchesFewMany JejunumIleum

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

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

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

General features of large intestine : Small intestineLarge intestine 1. Villi 2. Mucosal fold 3. Taenia coli 4. Haustra coli (sacculation) 5. Appendices epiploicae 6. Peritoneal relation 7. Peritoneal fold + Circular folds (plicae circulares) - Intraperitoneal organ (except duodenum) Mesentery proper (except duodenum) - Semilunar folds (plicae semilunares) +(except appendix & rectum) + + (except caecum & rectum) Retroperitoneal organ (except caecum, transverse colon, sigmoid colon & rectum) Transverse mesocolon Sigmoid mesocolon

Caecum : 7.5 x 6 cm., blind intestinal pouch, Rt. iliac fossa (L 5 ) 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

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

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

Ascending colon : 20 cm., Rt. lumbar region Rt. colic (hepatic) flexure Secondarily retroperitoneal organ Volvulus (L.volvo=to roll)

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

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

Sigmoid colon : 40 cm., S-shape, suprapubic region, intraperitoneal organ Rectosigmoid junction (15 cm. from anus, S 3 ) Sigmoid mesocolon (reverse V-shape) & intersigmoid fossa

Clinical consideration : Variation Sigmoid volvulus

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

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

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

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

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

Anorectal ring Anus, anal verge Levator ani muscle (pelvic diaphragm) 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 vagina Post. : anococcygeal raphe ’ Upper : pelvic diaphragm

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

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

Hemorrhoids or piles :